I've related this before, but I've had some super negative experiences with very entitled people. One person was a professor for whom I continued to build stats software for 18 months after leaving university. He actually repeatedly called me screaming when I was too busy to do some custom work for him on his timeframe. After giving him 10+ hours a week of free work for a year and a half because I thought the software was interesting and I believed in the work the various labs were doing.
I also work on a bit of open source software that I wrote that implements a high performance (threaded and heavily beaten on with vtune) ml algorithm.
I think the solution, particularly for small projects or individuals, is to preemptively cut people off. After many negative experiences, when I get bug reports or requests, if the reporter hasn't put in a reasonable amount of work already, I just killfile the email address and move on with my life. Even a small fraction of negative people was ruining any interest I had in working on my project: I'd open the tag in gmail, read a nasty or demanding email, and lose all motivation.
If people don't preemptively respect my time, I have no use for them. If they don't like that, they can have a full refund of everything they've paid me =P