When a dispute is started, funds are frozen by paypal. Buyer can send back a package with tracking, maybe with rocks in it, or an item similar to the purchased item, but worthless, or whatever. Paypal can see by the tracking that the package was returned to the seller, and money is refunded to the buyer. The practice is common enough that some ebay seller put identifying markings on items sold to keep buyers from returning a different item. Bad stuff happens all the time with paypal transactions. Just something to be aware of.