It is a game they play, small firms that go by "for and behalf" and shit like that. They just go about sending letters and scare tactics hoping that a few poor souls will actually send them payment, which they pocket, and the product you send them back too. It helps pay their rent space, utility bills, and secretaries pay, and on a good days collection, a night out in Manhattan ! It is a grey area, and technically legal. Don't even answer their Emails at all. Ignore them, they are just craigslist and ebay crocodiles on the prowl fishing for prey !