The cheapest solution would just be to add a thing to the T&C that says that Amazon reserves the right to place a reasonable number of undercover orders, which the vendor must accept as a refund (other than the shipping fees). Then Amazon is only on the hook for the shipping for one of every product they get a complaint on. That seems like a pretty reasonable amount for them, especially given that there is 0 shipping fee for anything from Amazon's fulfillment. Unless merchants are hiding these things inside the actual product box, instead of inside the shipping box. In that case, they should just ban the manufacturer's goods from Amazon entirely.