"It isn't so easy to determine if costs are covered."

I suppose I agree that it's not easy to attribute costs, but if this is a defense of Citibank or Trump's claims about Amazon, it seems like special pleading. If it isn't so easy to determine if costs are covered, and if the Post Office is not giving them any deal other major shippers don't get, and they are audited according to some standards that people defined as acceptable, then it seems as though people should stop claiming the USPS is subsidizing Amazon.