Responding as a buyer, and not offended at all. I sort of feel that with your solution Mipa (Oops, I meant Dragons Cavern), you’d just be transfering responsibility to the buyer. Some people are incapable of saying no, even if that is the way they really feel, which isn’t at all my case 😉 , but you might end up with bad feelings and as a selling artist, I’m guessing this is something you do not want to do.
I feel that if, while you’re painting a particular piece, you start thinking that it might sell well and that you might wish to reproduce it, or if you might do it because you can’t afford to refuse a paint job, just don’t bother with the OOAK. People asking for reproductions just proves that a lot of buyer don’t care if it’s OOAK or not as long as they like the final product.
You know what might be interesting? You might state in your auction that if there is interest, this paint job could be reproduced and the pieces would be numbered. As we’ve seen, the first of a series often sells as high as a OOAK and it also tells the runners-up that they could get one just like it. Just an idea.