Remove the human element. Yes, someone spent time fixing a bug. If the fix doesn't look like it makes sense on its own, do not merge it. If the author tries to convince you that it's a good fix, it's an immediate no.
A good fix (which is the only acceptable fix in open-source software), is one that speaks for itself.
Well, I dunno. Sometimes the fix speaks for itself but the other party is as dumb as a box of rocks and doesn’t understand. It can be hard to tell the difference.
> A good fix (which is the only acceptable fix in open-source software), is one that speaks for itself.
I disagree. Often if I'm making a PR to an open-source project I'm doing so because I have a use-case that the original author hadn't considered. So the first step in getting the PR merged is explaining my point of view and convincing the maintainer that my use-case is valid. Only when this is done can the "goodness" of the patch be evaluated.