They get an immediate response of not accepted, try again. Some buyers feel like they can say "are you sure you don't want to accept my offer?", or want to state that "It isn't worth what you are asking for", others just want to try to beg, and plead "Please, it's for the orphans, or the handicapped vets, or we just had a house fire and all my babies LEGO were destroyed.
Likely yes, but at that point you would have such a toxic transaction - that there would be no way that it would end well.
You can not force a buyer (or seller) to complete a transaction. Yes, they may get a ding on their account, but trying to force a transaction will not end well.
A seller is fairly helpless, so always proceed with some caution (and read the offers so it doesn't happen).