Buy it Now, or BIN locks you in to sell the domain for that exact price instantly and makes you liable to folllow through on that if a member wants it. .
However, Make an Offer is more liberal. You can take offers "till the cows come home" and not have to follow through on any of them. Owners of "liquid domains" have been using this lately almost exclusively to gauge how much they can get since they do not have to follow through on any of them.