PP and credit cards payments, always an interesting topic when debated by those in this hobby.
The convenience of being able to take PP or credit card payments really opens up the door for those sellers doing so. It also makes payments instantaneous. There are some risks, such as charge backs, but that is probably rare. However, with that convenience comes a price. The fees are what enables those sellers to accept credit cards where they otherwise would not be able to do so or where they would need their own machine and likely pay more.
HOWEVER, many sellers in this hobby are not true businesses and most of the money they make is probably used to buy more cards. Many of these people are trying to avoid paying the fees by charging more to cover their fees (something ebay made illegal long ago), switching it around so the buyer pays the fees (gift transactions, etc), etc.
It all comes down to what expense a buyer is really willing to assume when buying from these people. Sometimes I am willing, other times I am not. I'm already paying a cost for the item and a shipping charge. Sometimes there is even a handling charge as well. If the buyer wants to sell me his card, maybe he needs to pay that PP fee.