> If I then factored the resulting number, these people would then tweak the formula again and insist that they had fixed it.
Along with each successive refutation, you should require them to include a cheque for double the last amount with their next fix, starting with a reasonable $25.
It would make them think twice about using the reviewer as a cheap refutation engine. Perhaps even make them try to refute themselves. Which would be a win for everybody.
