EBay depends on members to police the site. There is a Report button on every listing. When you use it, you get a polite thank you note from eBay. There will be no further contact, but you have put the listing on the radar and eBay does act, especially when the violation costs them money.
Paypal itself has a Buyer Protection Plan almost as strong as eBay's. If you were defrauded by an off-eBay seller, go to your Paypal account and look in the top right corner for the Security link. Follow through as you would on eBay, the processes are very similar.
Like eBay you only have 45 days for this.
If more than 45 days have passed, go to the credit card you actually used to pay (PP is only the mediator) phone the 1-800 credit card number and ask about a chargeback. The clerk will need transaction numbers, dates and payment amounts to make your refund.