One of our suppliers puts the below links on their request closure emails which we have always liked, I know Manage Engine ServiceDesk Plus sends out surveys but having something like the below where the requester can optionally leave feedback for any of their call logs and that feedback is recorded against individual request would be great.

 

When the requester clicks one of these buttons they get a web popup and they can leave an additional comment, again this should be recorded again the request.

 

Then a report or two to get a general summary of call feedback