it's great, unless you're on the other side of the fence. a customer decides that you don't deserve the money for the product you shipped, and requests the money back. without even bothering to clarify what's wrong. and there's absolutely nothing you can do about it.

well, technically there is, but is it worth 5-10£ in losses? no. and you loose. and customer gains. everyone's happy.

PS. I'm ranting, because my wife just sold on her online shop something to a customer, who then went to a bank and said they can't remember making this payment. so bank charged paypal, and paypal removed the funds. we raised a dispute, but got a standard answer of 'wait 75days and see what the bank decides, the decision will be final. bye.'