I had a not-too-interesting answer on Stack Overflow, which was closed as duplicate after some clarification by OP.
After a day or so, OP (a ~700 reputation user) started complaining that the question turned into a "down vote magnet" (it just received three down votes in the first minutes and none afterwards). He asked me and another user to delete our posts, which I thought was not fair to the other user (with quite less reputation than me).
After some more complaints I just saw the question was deleted by a moderator, without a clue why. I guess OP flagged the post and asked the moderator to delete it.
This action seems unfair to users spending their time to compose an answer. It allows those asking poor questions to get away with no 'reputation penalty'.
That made me wondering if there is an official policy on this. Can posts 'just' be deleted on request? What are (or should be) the rules for questions to be deleted in this way?