Very odd for sure, I too thought only the Seller or Ebay could mark it as payment received. If you have a international shipment, the seller has to invoice, ebay will not this will allow you to change the shipping price. I ship international all the time and I look at each order details when it is sold and when I get a international I add the shipping cost, it is left blank on the invoice and don't think the buyer can pay until you have adjusted the cost. Not sure what you have going on, but sounds a bit strange to me. I don't buy too much on ebay I wander if the buyer can mark payment received, I will have to look next time I buy. Thanks for the heads up on the situation something to watch for sure.