Easily? You think the kind of people who think it makes sense to make bogus slop PRs are going to react reasonably to overburdened volunteer maintainers refusing to give them their US$10 back?
This is never going to work. Sufficiently many of these people are going to find maintainers' home addresses and send them death threats and the likes. If you see how badly some people flip out just because their PR is rejected, it's going to be much much worse if their PR is rejected and their money is taken.
Ok. If I'm the maintainer receiving death threats over that, I'd tell them they would get the $10 dollars back, plus some extra money for their troubles.
Location of the envelope with the money: the same police station where I'd reported the death threats.
I don't think that is a (very realistic) concern. AI is slop, the problem is not that the real contributors are struggling to get PRs merged.
The bigger issue being, raising the bar to students who may have otherwise had productive careers (but education is a general issue, where the students don't even yet recognize they are being scammed).
I don't follow, and I'd be concerned that this opens up a cottage industry of bots generating plausible looking repositories that unwitting contributors would attempt to contribute to. We already know that bots are astroturfing repos to generate overinflated star counts. I'd say the least crap option here is to honeypot PR contributions from bots
You keep describing this as not a likely or realistic scenario. But why is the likelihood even of relevance here? The way to avoid the worst case i.e scammed of your money, is to not even put it on the table in the first place.
Let's also be realistic, everything that can be automated will. Even if that thing is worse off for it. There's a clear historic pattern of this. Companies and people love to be penny wise and pound foolish.
You also lose out on a lot of would-be PRs. By people who don't have the money, don't have trust, or have a visceral "fuck you" stance. There's a lot more reasons that this suggestion creates a gate that dissuades the people you want. I stand by that the solution is naïve, but you're welcome to give it a try on your projects. I'm sure it'll be effective at reducing a lot of spammers, but I'm also pretty convinced it'll come with a large false positive rate, which is invisible (giving you false confidence)