Your return only policy is
Your return only policy is rotten. Exchanges should be allowed. If you buy a shoe on sale, but it does not fit you cannot exchange it. You have to return it, then buy a new pair in a different size. The problem is that you will not be getting the sale price. If you wait until another sale, you may not get the shoe you want.
Exchanges should be allowed. If the shoe you want to exchange is not available, then a refund can be given. At least let people have the option to try and get an exchange.