Recently I also purchase on ioffer through paypal. People from San Jose California, real email, and of course paypal acepted. I bought a 1500 laptop, what they sent me was a plug adapter for a cell phone. I filed a dispute, the scammers escalated it and produced a tracking number. The short story is that since i did not buy at ebay, I was not protected. The fact that I got something in the mail was OK with them, so they closed the case and refused to reverse the transaction. I would not buy anything with paypal from now on. I am not asking the bank to step in on this, hope it works.
You should reproduce the postal manifest of what the item was. The weight of the adapter is much much lighter than the weight of the laptop. The manifest should have that in the record. Base on that, you can argue that you did not receive the item you bought. Paypal has record of the correct item you bought (i.e. the laptop) and you can get the weight specification from the manufacturer.
Now that the scammers showed up, it's your opportunity to further escalate it to your credit bank.
I would not pay that amount and let this credit card company file a collection against me and I will show them evidence that that was a fraudulent transaction and they should further investigate. I would report them to FTC.