As a buyer, the transaction fee should not be carried onto you. The few times I have seen sellers charge extra to use PayPal, there was a cheaper alternative, like paying with credit card, direct deposit, or mailing a check.
As a seller, you can lower transaction fees by using a merchant services provider instead of PayPal.
Personally, I’m excited for blockchain companies like Request Network that could push transaction fees much lower (~0.1%). But this technology is still in the early stages.