What exactly do you mean by this? Do you mean buyers who send you money, but then want their money back? If so, it's always best for business to offer a guarantee. This establishes trust and if people take you up on the guarantee, you should honor it. However, if people are getting around things in a way to harm your business, you should find a way to stop that or ban the users. Most people are good though, so this should be a minority of people.