My guess, too.
Or maybe something like "Its all free, but we'll give you $1500 to cover shipping, but shipping will only be $500. So we'll send you $1500, then you take $500 to give to the shipping company, and then give us back $1000" or some other fuzzy math scam where they give you a fake check, you cash it, give them money, then it bounces and you're out the money.