PayPal fees are a cost of doing business FOR the business. Just like the fees that sellers have to pay in order to have a credit card account.
Just tell the sellers that unless they are "friends and family" and the money is a bonafide gift, then they just don't qualify to receive funds in that manner. If they want to become "friends", then how about a "friendly" discount, buddy?
If they argue with you, just terminate the conversation and find what you want elsewhere. If more people act in this manner, the problem will eventually become self resolving.
I buy a fair number of items on the net using PayPal, and I have NEVER, EVER had any seller insist on this sort of nonsense.
I get dinged by fees on every transaction made for memberships, sponsorships, and advertising from my FaunaAds.com website. Do I like having to lose that money to fees? Nope. But I would like it even less if there wasn't an online function like PayPal to process those payments easily and conveniently. They need to make money in order to stay in business. That's just the way it is. Ya wanna play, ya gotta pay.