I agree, unless a full and complete refund of all money paid was an option I would not even consider it. I would also want a "get out" clause- supposing the foal was nice, but you just did not like it?? In that case, of course you would lose your deposit, that's only fair, but you should be able to walk away still friends. BTW a "Foetus" was auctioned at a Sport Horse sale recently- it was inside a Surrogate, and it made $22,000.00 !! The Surrogate was to foal (at new owners risk of losing the foal, but the mare was fully insured) raise the foal and then return to sender!!
It's not something I would normally do, either to buy or sell,