We do tell, but not too often. There are a few reasons for this:
- often the final hire/no hire decision is made several minutes/hours after the last interview of the day, and the person has already left. In this case it would be the recruiter/HR person who will be informing them about the results. Assuming that the candidate would like to ask follow-up questions or have a discussion about his/her interview, the recruiter will probably not be able to continue such a discussion;
- in cases when "no hire" decision is made on the spot, it is quite often done because of candidate's attitude. It would not be a good idea to discuss negative personal qualities of the candidate for obvious reasons.
Sometimes (~5-10% of cases) I do get a chance to tell the reasons for my decision, and that always happens when I feel the candidate will benefit and/or improve based on the feedback, and when this improvement is possible. Example: the candidate shows good aptitude and stable personality, but lacks knowledge in the specific area we require. Sometimes it's a matter of more experience, but sometimes it's because candidate's interests are in a different field. I never do it when the candidate is arrogant, seems emotionally unbalanced, or is caught lying.
In any case, we try to leave our business cards, so we can be contacted for feedback via e-mail or phone call. I very rarely get questions this way, but when I do, I always answer politely and as directly as I can without giving reasons to sue.