So a scammer just tells PayPal "my account was hacked" and gets money back at sellers penalty with no investigation? If sold on eBay means eBay account was hacked + associated PayPal account hacked + record of actual payment to provided bitcoin address in payment note.
hmmm.. PayPal people must be pretty stupid...
No, they aren't stupid. It is purely business. The seller assumes the risk of fraud. PayPal has to side with someone, so they usually side with the buyer. They don't gain much from investigating.
Outside of ebay (craigslist, for example), there are man-in-the-middle scams. The scammer agrees to buy bitcoins from you and to sell something to someone else. They give the other person your paypal account. Then the other person sends you the money and you send the bitcoins to the scammer. When the other person doesn't receive the item they bought, they get contact PayPal and get their money back (note they were actually scammed in this case). The scammer keeps your bitcoins.