I agree that most sellers adding PayPal fees, really want F&F payment, thinking that it gives them total control over the transaction, in case anything goes wrong.Could be lazyness or nickle and diming. Some will even ask for 4%, 4.5%, 5% or whatever percent they want for whatever reason.
I think they put it to entice/fish for a "discount" via F&F.
Those individuals could unknowingly be setting themselves up for a credit card chargeback, from a shady buyer, having that control taken away from them, and also losing their knife.