If you are a private seller then no you don't have to agree to a return if an item doesn't fit. However, some crafty buyers will invent a fault with the item, in which case you will not only be forced to accept the return and give a refund, but you'll have to pay the return postage too. Some times it's better to cut your losses, even though it's not always fair.
If you are a business seller, then yes you do have to accept a return, and pay for the return postage.
