millhous
“but if you structure the sale so that if the buyer doesn’t pay it reverts then retroactively you owned chometz on Pesach”
Incorrct, as has been explaind svral tims over several years in this thread
“That is the way every sale I’ve witnessed has been done”
Have a look at sample contracts, for example printed in kitzur.
“He has to pay up, and we can absolutely sue him for it.”
This seems addressed to me, but i explicitly said that already “Yes, and there is no question he halachicly owes me the money, and while I’m no lawyer I believe legally as well, exactly as you say.” So I’m not sure why you are repeating that.
You comment about Arav kablan, is EXACTLY to alleviate my concern, but its use is controversial and most (chabad being a notable exception do not use on)