Well said Thsalmon! I fail to see why the seller would have to absorb this charge when Paypal is chosen by the buyer as the method of payment. If the buyer doesn't want to absorb the Paypal charge then he just has to go with another payment method. My answer would differ though if Paypal was the only method of payment accepted by the seller or if the seller insisted on Paypal being used for payment. In any event, there is a very simple solution to your problem: simply ignore the ads where the seller is asking the buyer to assume the Paypal charge or just don't use Paypal for payment.
PayPal Surcharge
I have noticed alot of people add a (3% or so) PayPal fee to their items and I wonder if everyone is aware, that is against the user agreement. It seems that PayPal looks at sellers as "merchants". This is cut from the Paypal website:
-No Surcharges. Under Visa, MasterCard, Discover and American Express regulations and the laws of several states, including California, merchants may not charge a fee to the buyer for accepting credit card payments (often called a "surcharge"). You agree that you will not impose a surcharge or any other fee for accepting PayPal as payment. This restriction does not prevent you from imposing a handling fee in connection with the sale of goods or services, as long as the handling fee does not operate as a surcharge (in other words, the handling fee for transactions paid through PayPal may not be higher than the handling fee for transactions paid through other payment methods). Nor does this restriction apply to Pound-denominated transactions by sellers residing in the United Kingdom listing items for sale on a UK-based website.
-No Surcharges. Under Visa, MasterCard, Discover and American Express regulations and the laws of several states, including California, merchants may not charge a fee to the buyer for accepting credit card payments (often called a "surcharge"). You agree that you will not impose a surcharge or any other fee for accepting PayPal as payment. This restriction does not prevent you from imposing a handling fee in connection with the sale of goods or services, as long as the handling fee does not operate as a surcharge (in other words, the handling fee for transactions paid through PayPal may not be higher than the handling fee for transactions paid through other payment methods). Nor does this restriction apply to Pound-denominated transactions by sellers residing in the United Kingdom listing items for sale on a UK-based website.