I am fairly sure that trafficking in stolen goods is only a crime if the person knew, or if a reasonable person should have known, that the goods were stolen.
I don't know if it's a crime if it's just "somewhere we must be buying stolen goods, but we don't know where." I'm not a lawyer but I think knowing that the specific item you bought/sold was stolen would look differently in court than just having some vague knowledge there must be stolen stuff somewhere in the supply chain.
Either way, if you possess stolen goods, they will usually be taken from you and returned to their owner. If that happened to a lot of Amazon customers, the refund volume would encourage Amazon to crack down on their supply chain.