Are you thinking something like
"I have a $50 USD giftcard at JC Pennys" and you quote them $35 for it, then arrange payment and transfer?
a few questions
- do you have a design template you already want to use?
- are you aware that once they agree to sell it to you, they can still write down the number and use it online, after receiving your payment and transferring it out of their paypal so you cant get it back?
- do you have the process thought out on how you want it handled (the flow of the site)?