If a buyer makes an offer on a house, is he/she bound to it?

A buyer can withdraw an offer anytime up until the offer is accepted by the seller. After that, the seller may owe the commission to the broker, and may well turn around and sue the buyer for breach of contract to recover the cost of that commission.

If the seller changes his/her mind after accepting an offer, especially if the terms of the listing agreement have been met, s/he usually still owes the broker a commission. This depends largely on the wording of the listing agreement; it might be wise to state that the commission will be paid upon completion of the sale of the property.