How do the nigerian 23432 scams work when you are going through paypal?

i am trying to sell a ps3 and i got a bunch of emails from folks who want the items shipped internationally, most to nigeria. after looking around the net i found a lot of these nigerian scams. my question is, if the payment is made through pay-pal how can they scam me. i don’t give them any user name or password. all i send is emails and a request for money.

They will likely send you a fake email from "PayPal" that claims that the money has been sent but won’t actually be released into your account until shipment is confirmed.