if i signed up for paypal on another site can i still use it for selling credits

Yes. If you want to sell credits here and use Paypal you just have to PM them with your paypal email address.  Just be careful if you're going to accept credit cards that you make the deal decent enough to cover the fees. I  had someone want to buy 2 credits once.  She used a credit card and goofed up the amount and did it twice. So it wanted to charge me twice to accept the funds.  I ended up only accepting one and basically ended only getting like $2/credit.  So now I only sell them if the person is using their checking account or is buying enough credits to make the fee worthwhile. 

what is the fee

If they use their checking account there's a .50 fee to tranfer the money to your PBS account. No fee if you use it to buy something on Ebay.  But for credit cards they charge like a .30fee and then a % that depends on the account you have. You can find that out on the paypal website.  So if they buy a bunch of credits, it's worth the fee to accept a credit card. But if they just buy 1 or 2 by the time you pay the fees-not worth it unless they add the fee into their cost.

thank you