PayPal transactions are reversible while Bitcoin transactions are irreversible. You want someone to send you an irreversible payment first and trust you with over a thousand dollars and you send them a reversible payment later? I'm not accusing you of anything, but would you do it if you were on the other end of the deal? And would you use escrow?
Btw, there are other exchanges like localbitcoins where they sell you btc for PayPal and they have their own ways to verify if you are legitimate so you won't have a problem there I guess