Thats why you should always put in a return policy that says (1) the item must be returned and you may want to put some special markings on the product to ensure that its your actual product and the scumbag trying to not to pass off their broken one and (2) never send out any replacement until you get the one back. If the item was 30 days and you knew it was working perfectly, then you knew that it was the buyer that either broke the item or made a claim that was false. Its always buyers know the warranty period and think it doesn't pertain to them. They can have it for 10 years and then think they can return it. Save the emails, and put them in a logical order, simple state you offered to fix it for free but the buyer refused to return it. If the buyer doesnt return it they get shit !