Checked out Mike Wilbank's site, didn't see anything about covering fees, but it is a big site. Chris, can you locate that?
Just checked out Bob Clark, didn't see anything about Paypal fees.
However, in order to make an informed decision about claims of sellers who in years past charged customers for Paypal fees, one would have to be able to view the Paypal TOS for that time period. Paypal TOS has evolved over the years.
In fact, I think Paypal would do something about those violating their TOS. They have quite a list of what they are able to do to those violating the various items listed in their TOS, including withdrawing the seller's ability to use Paypal as a payment method. That might be a huge strike against a business, particularly an online business, whose customers do not want to give out a credit card number.
from Paypal:
4.5 No Surcharges. You agree that you will not impose a surcharge or any other fee for accepting PayPal as a payment method. You may charge a handling fee in connection with the sale of goods or services as long as the handling fee does not operate as a surcharge and is not higher than the handling fee you charge for non-PayPal transactions.