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I recently experienced annoying and imho exploitative behavior from a new user, which persisted after I tried to explain to him how SO works. The question is how to deal with this.
long-winded narrative: To start it off, he posted small variations of the same, badly formulated and ill-defined question again and again because he didn't receive answers as quickly as he'd wanted. Through a lengthy exchange of comments, I finally managed to get him to improve his question. I then invested quite some time to come up with a solution and posted a long and as far as I can tell comprehensive solution. He showed himself impressed and glad about the solution, and upvoted and accepted my answer. Shortly after, he asked an additional question, first as a comment on my answer, then as a new SO question, and asked me to answer that one, too. When I didn't respond immediately, he accepted another answer to the first question (thereby unaccepting mine), one that had been there before and apparently hadn't been the solution. I complained, he again accepted my answer, and again bugged me to answer his second question. When I didn't do that, he again accepted the other answer thereby unaccepting mine.
Don't get me wrong, I completely understand that it is the OP's prerogative to decide which answer is correct/best and therefore should be accepted. I never questioned an OP's decision before, even when I felt I actually deserved the credit. But, I think this behavior shows that the poster is not interested in marking the best answer, but uses acceptance like a carrot dangling in front of others, to push them to immediately and completely give him whatever he wants at the moment. I pointed out to him how SO is supposed to work, but he completely ignored those hints, so it appears he is utterly uninterested in the whole idea of "good questions, good answers". Moreover, I feel taken advantage of, because I put much effort into first helping to clarify the question and then answering it thoroughly, without lasting recognition.
My question is: How would you recommend to deal with such a situation? – Play the missionary and bug such a user with more comments pointing out the wrongness of his ways? Suck it up, because there will always be exploitative people and there's nothing that can be done about it? Just ignore questions that appear to predict such a pattern of behavior? Or go the flagging way ("duplicate", "unclear what you're asking") from the beginning without trying to help individually (I really don't like that, it feels rude to me)?