Description of problem:
With yum, if you had a dep solving conflict, you'd get info like:
--> Running transaction check 
---> Package firefox.i386 0:3.0.7-1.el5 set to be updated 
--> Processing Dependency: xulrunner >= 1.9.0.7-1 for package: firefox 
--> Running transaction check 
---> Package xulrunner.i386 0:1.9.0.7-3.el5 set to be updated 
--> Processing Dependency: xulrunner = 1.9.0.5-1.el5_2 for package: xulrunner-devel 
--> Finished Dependency Resolution 
xulrunner-devel-1.9.0.5-1.el5_2.i386 from installed has depsolving problems 
  --> Missing Dependency: xulrunner = 1.9.0.5-1.el5_2 is needed by package xulrunner-devel-1.9.0.5-1.el5_2.i386 (installed) 
Error: Missing Dependency: xulrunner = 1.9.0.5-1.el5_2 is needed by package xulrunner-devel-1.9.0.5-1.el5_2.i386 (installed) 


Or

--> Processing Dependency: python(abi) = 2.4 for package: python-paramiko-1.7.6-1.el5.rf.noarch
--> Finished Dependency Resolution
Error: Package: python-paramiko-1.7.6-1.el5.rf.noarch (rpmforge)
           Requires: python(abi) = 2.4
           Installed: python-2.6.6-52.el6.x86_64 (@rhel-6-server-rpms)
               python(abi) = 2.6
           Available: python-2.6.5-3.el6.i686 (rhel-6-server-rpms)
               python(abi) = 2.6
           Available: python-2.6.5-3.el6_0.2.i686 (rhel-6-server-rpms)
               python(abi) = 2.6
           Available: python-2.6.6-20.el6.x86_64 (rhel-6-server-rpms)
               python(abi) = 2.6
           Available: python-2.6.6-29.el6.x86_64 (rhel-6-server-rpms)
               python(abi) = 2.6
           Available: python-2.6.6-29.el6_2.2.x86_64 (rhel-6-server-rpms)
               python(abi) = 2.6
           Available: python-2.6.6-29.el6_3.3.x86_64 (rhel-6-server-rpms)
               python(abi) = 2.6
           Available: python-2.6.6-36.el6.x86_64 (rhel-6-server-rpms)
               python(abi) = 2.6
           Available: python-2.6.6-37.el6_4.x86_64 (rhel-6-server-rpms)
               python(abi) = 2.6
           Available: python-2.6.6-51.el6.x86_64 (rhel-6-server-rpms)
               python(abi) = 2.6
Error: Package: git-1.7.12.4-1.el5.rf.x86_64 (rpmforge)
           Requires: libcurl.so.3()(64bit)
Error: Package: perl-Git-1.7.12.4-1.el5.rf.x86_64 (rpmforge)
           Requires: perl(SVN::Client)



With dnf, it just says there's an issue:
[root@pmg-w541 ~]# dnf update libcmis
Last metadata expiration check performed 0:16:56 ago on Mon Sep 14 08:47:40 2015.
Dependencies resolved.
=============================================================================================================================================================================================================================================
 Package                                                       Arch                                                 Version                                                       Repository                                            Size
=============================================================================================================================================================================================================================================
Skipping packages with conflicts:
(add '--best --allowerasing' to command line to force their upgrade):
 boost-date-time                                               x86_64                                               1.59.0-3.fc24                                                 fedora                                                60 k
 libcmis                                                       x86_64                                               0.5.0-9.fc24                                                  fedora                                               536 k

Transaction Summary
=============================================================================================================================================================================================================================================

Nothing to do.
Complete!

# rpm -q boost-date-time libcmis
boost-date-time-1.58.0-9.fc24.x86_64
libcmis-0.5.0-8.fc24.x86_64

# dnf update boost-date-time
Last metadata expiration check performed 0:19:57 ago on Mon Sep 14 08:47:40 2015.
Dependencies resolved.
=============================================================================================================================================================================================================================================
 Package                                                       Arch                                                 Version                                                       Repository                                            Size
=============================================================================================================================================================================================================================================
Skipping packages with conflicts:
(add '--best --allowerasing' to command line to force their upgrade):
 boost-date-time                                               x86_64                                               1.59.0-3.fc24                                                 fedora                                                60 k
 libcmis                                                       x86_64                                               0.5.0-9.fc24                                                  fedora                                               536 k

Transaction Summary
=============================================================================================================================================================================================================================================

Nothing to do.
Complete!

It'd be nice to get more info on what the problem is. I have older versions of both boost-date-time and libcmis installed than what is trying to get pulled down, so which updated package needs a different version of the other package? 


Version-Release number of selected component (if applicable):
dnf-1.1.1-2.fc24.noarch


How reproducible:
If there are dependency issues, 100%

Steps to Reproduce:
1. Try to update a package that causes dependency issues
2.
3.

Actual results:
# dnf update boost-date-time
Last metadata expiration check performed 0:19:57 ago on Mon Sep 14 08:47:40 2015.
Dependencies resolved.
=============================================================================================================================================================================================================================================
 Package                                                       Arch                                                 Version                                                       Repository                                            Size
=============================================================================================================================================================================================================================================
Skipping packages with conflicts:
(add '--best --allowerasing' to command line to force their upgrade):
 boost-date-time                                               x86_64                                               1.59.0-3.fc24                                                 fedora                                                60 k
 libcmis                                                       x86_64                                               0.5.0-9.fc24                                                  fedora                                               536 k

Transaction Summary
=============================================================================================================================================================================================================================================

Nothing to do.
Complete!


Expected results:
Output like the yum examples at the start which list what is needed and required. 

Additional info:
Using --best then mentions another package, libkolabxml, that isn't mentioned in the dnf update output.
# dnf update libcmis --best
Last metadata expiration check performed 0:58:38 ago on Mon Sep 14 08:47:40 2015.
Error: package libkolabxml-1.0.3-4.fc24.x86_64 requires libboost_system.so.1.58.0()(64bit), but none of the providers can be installed
(try to add '--allowerasing' to command line to replace conflicting packages)


This might be better suited for another bug, but having --allowerasing should come with big warnings.
# dnf update libcmis --best --allowerasing
Last metadata expiration check performed 0:59:28 ago on Mon Sep 14 08:47:40 2015.
Dependencies resolved.
=============================================================================================================================================================================================================================================
 Package                                                        Arch                                               Version                                                         Repository                                           Size
=============================================================================================================================================================================================================================================
Upgrading:
 boost-date-time                                                x86_64                                             1.59.0-3.fc24                                                   fedora                                               60 k
 libcmis                                                        x86_64                                             0.5.0-9.fc24                                                    fedora                                              536 k
Removing:
 libreoffice-calc                                               x86_64                                             1:5.0.1.2-1.fc24                                                @System                                              29 M
 libreoffice-core                                               x86_64                                             1:5.0.1.2-1.fc24                                                @System                                             236 M
 libreoffice-pyuno                                              x86_64                                             1:5.0.1.2-1.fc24                                                @System                                             1.9 M
 libreoffice-writer                                             x86_64                                             1:5.0.1.2-1.fc24                                                @System                                              15 M

Transaction Summary
=============================================================================================================================================================================================================================================
Upgrade  2 Packages
Remove   4 Packages

Total download size: 597 k
Is this ok [y/N]: 

It could be easy to see the output in your dnf update,
Skipping packages with conflicts:
(add '--best --allowerasing' to command line to force their upgrade):
and then the user think that they need to update so they should just tack that on and then miss that a number of their packages would get removed.