Charging back a PayPal transaction also basically ensures you'll get banned from the service (and by extension: eBay)
It's not credit card -> merchant, but rather credit card -> your PayPal account -> merchant's PayPal account
Edit: What I mean to say is that AFAIK, paying by CC through PayPal is separate from your PayPal balance.
The point being made is that your CC transaction is still with PayPal, so if you chargeback they might ban you from the service.
Charging back a PayPal transaction also basically ensures you'll get banned from the service (and by extension: eBay)