Can You Be Asked for Proof During a Border Bounce at Mae Sai?

As people said, in theory you could be asked but that border crossing doesn't ask at all.

They check to make sure you're of a nationality that can bounce there, that you haven't used your two 30 day visa exempt entries yet and then stamp you out of thailand.

it's an easy border to bounce at.

Anyone on any visa or exempt COULD be asked, but in practice very very few are. If you’re trying a third or forth attempt at a tourist visa / exempt in a row then you’ll raise the suspicion of the immigration officer and may well be asked. More often than not at an airport rather than land border, which are generally more relaxed. But you could be. If you’re worried have the proofs.

You could be asked, but you won't.

Never happened to me. Did it 3-4 times.

Its always best to be prepared...just in case you are asked. And if you have a history of border bounces, visas and extensions...might be asked. Good luck.