My experience is if you send the package with tracking and requiring a signature, they cant say it was never delivered because you have proof.

Second take as many pictures as possible of what you are selling. They cant say its wrong if you said im selling whats pictures, and they signed it when it came in saying it was the right item. Just make a disclaimer on the box to say, Do not sign unless item is as received.

Ive never had much problems with paypal. I feel they charge way to much, being owned by EBAY and all. Its a big hassle, but make sure you can prove you are right every time.