I always wondered why anyone was willing to sell it via paypal,but assumed they just needed to log the comms and record blockchain info in case I tried to reverse it. It wouldnt be hard to prove the transaction went through.
You can prove the transaction went through just fine, but that isn't enough evidence for Paypal to rule in your favor.
Even if you printed a paper wallet and shipped it with delivery confirmation and signature, Paypal still won't rule in your favor. It's an automatic easy-to-win dispute for the buyer which is why there are so many scammers doing it now. You also have hacked Paypal accounts where they use BTC to cash out. They can' t just transfer to other paypal accounts and cash out because eventually there will be a bank account or credit card that connects to a real user (plus Paypal limits on transferring to/from unverified accounts). But use the Paypal account to buy BTC or other virtual goods (MMO in-game virtual currency) and then you can transfer the virtual goods around without being traced.