First, decide why you don't want this: Is this a "patches welcome" situation where the change is good but not worth your time, or a change that would make the s

First, decide why you don't want this: Is this a "patches welcome" situation where the change is good but not worth your time, or a change that would make the software worse/isn't a good fit? Then explain that politely but firmly, and don't be afraid to explain that you're a volunteer working on it, so you ultimately make the calls. If the reporter becomes uncivil, close and lock the issue. If they start being disruptive/filing new issues, ban them. (You could also offer paid support, but it seems like you already know that this person wouldn't be a nice customer to work for.)