You'll be paying via BitPay so you'll get order number + email receipt, similar to paypal, except you'll also have blockchain tx id as an extra proof.
I don't know how a blockchain tx id is proof of anything. A seller could just say it was not their address. How do you prove it was theirs? Anyone can create a bitcoin address, there is no requirement to show legal ID or anything else. Bitcoin has zero proof of actual underlying physical identify of the sender or the receiver of a bitcoin transaction.
I could start a website selling gold myself. A buyer comes in, I create a new address and tell them to send their bitcoins. They send the bitcoins. I tell them I never received the bitcoins and it wasn't my address.
Now, go to court to try and prove that the address way my address. You can't. You may have an email chain that says something. But I would have an email chain that had a different address in it, I'd just modify the email.
How are you going to prove I received your bitcoins?
As I said, it's an additional proof. You could take screenshot of BitPay screen with specific payment address (and order number) to which you sent bitcoins to etc.
But yes, you can use pseudonymous nature of Bitcoin to scam people, it's a well known fact, but you could do the same with paypal/bank accounts registered under fake personal details not to mention cash transactions.
I don't recall anyone ever claiming to get scammed by any of the major BTC payment processors.
