I don’t see a problem with that, but may be that’s because I don’t know how the postal service systems handle transactions and revenues. For the scenario pointed out by the OP, let’s just say that these Chinese sellers will instead shipping their products using the regular first class mail – would the USPS then be able to collect/extract any revenue from it? Another way of looking at it is when I send a letter to a foreign country using the USPS first-class mail, is that foreign country be able to collect any $$ for the cost of processing and delivering the mail? I think if anything, it’s very clever for the USPS to figure out a way to tap into a potentially lucrative stream of revenue.