Short answer: you can't avoid getting scammed if you accept PayPal, even if you get paid well before you ship. If the buyer uses a credit card to back up his payment, he can dispute the charge with his credit card company and get a refund even months later. You end up getting hit with the chargeback fees from both PayPal and the credit card company, as well as losing the price of the merchandise. Scammers have been playing this game for years, and for more than just critters.
Here is just one example, there are many more if you search:
http://www.faunaclassifieds.com/foru...d.php?t=554519
Obviously shipping anything before getting paid is a nonstarter, as is shipping on a Thursday for Friday delivery. I had a snake take two days to arrive this past summer due to FedEx's screw-up.
The best way to protect yourself is to accept payment only via USPS MO or personal check, then wait for it to clear. If you set up as a business you can accept credit cards directly so if there is a dispute you are in direct contact with a merchant processor.