"Buyer pays fees"
So many classified ads "buyer pays paypal fees" - "add 5% if paying by goods/services" - "price not including PP".
Even though it says right here in PP ToS: 4.6 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
It was discussed as a forum rule previously, and isnt peculiar to airsoft, it happens everywhere and a solution was found by mothers who are fond of traditional terry cloth nappies
https://airsoft-forums.uk/topic/41707-paypal-fees/?tab=comments#comment-309821
http://www.clothnappytree.com/ppcalculator/
It’s common for sellers to ask that the buyer covers fees, but in doing so if they are not fully up front then it’s just messing people about.