The bitcoin sale will be a personal agreement between you and the buyer. Paypal is the payment medium for selling an envelope or something. When you get paid for the envelope, you send the buyer bitcoin along with the envelope. Paypal does not know that bitcoin is involved in the transaction.
Actually paypal don't create chargebacks, buyer need to be trusted to not open any charge backs against his payment to you. In terms of sales of goods buyer can file chargeback upto 180 days from the date of payment so when buyers will have bitcoin they can instantly create chargeback and most of the time buyers will win. What proof you will show paypal that you have actually delivered goods to buyer? also paypal will not believe that you are sending empty envelope for $100.
That 180 days to file a charge back thing was the point of my original post. What's stopping the buyer from filing a charge back with any other item? Nothing. So why are people extra paranoid about selling bitcoin but not as paranoid about physical items? What makes bitcoin so prone to charge backs more than any other item?
And it doesn't have to be an empty envelope for $100. I can send the buyer an empty envelope but tell paypal that it is a gift card being sold. That way the weight and price of the shipped item will not seem absurd.