I've lost my 8th case in a row today with Paypal, losing $1200 total.  This is about 10% of all my bitcoin transactions last 2 months.

As careful as I am with checking buyer is verified Paypal address, ebay account is aged (ignore the positive reviews you can't leave negative buyer reviews anymore), etc. you can still be scammed in 2 common ways:

- Buyer is the actual buyer and just wants to defraud you, so they will dispute a charge with Paypal or their credit card (or both)

- Buyer's account was hacked and the actual 'unauthorized' dispute is legitimate, but your virtual or physical goods were already shipped

Don't believe the Paypal seller protection.  Even if you ship physical goods with delivery confirmation (I had 10 lines of evidence in several cases), Paypal will automatically screw the seller in many cases including any credit card dispute or anything with the word 'bitcon' in it (even if you ship hardware).  Don't believe the Paypal press that they are supporters of bitcoin.  What they are is risk-adverse and will look to screw the seller at every opportunity at any sign of a dispute no matter how flimsy the evidence.

I saw a buyer dispute 16 Paypal transactions (by checking the feedback history on ebay and contacting each one).  We all received dispute notices the same day.  Buyer won all of them.  Yeah, right, buyer makes 16 separate ebay transactions with Q&A and delivery acknowledgment and it's us 16 sellers that are the scammer.  Paypal doesn't care about sellers.