I think you probably mean "commit to buy". This is a legal binding contract, and you cannot cancel. Sellers are sick and tired of people who "accidentally" buy things. They are charged fees the minute you buy. The listing then ends because you have purchased it, and then you expect the poor seller to relist the item and pay another relisting fee and then try to get back the fees from ebay, all the while they have probably missed out on selling to someone else.
