You can look at how the maintainer dealt with previous bug reports to decide whether you can trust them or not. If there haven't been any previous bug reports but they nonetheless ask for a fee to help deal with the large volume of bug reports, yeah, that might be a scam. If you're running their software, maybe also check whether it's full of malware.

Good scammers pay out once in a while. Casinos hate it when everbody body loses, and love it when one person wins big - they need just enough losers to make money while enough winners to show off.