In the Amazon case, it's not a big deal if both me and the shady seller communicate out of band. We can use email or whatever to orchestrate the payback for a positive review, and the penalities for our scheme being compromised are low: maybe we get banned from Amazon and frowned at by our friends, who cares.
In a darknet market scenario, we rely on the market to handle our identities, and try to stay completely anonymous otherwise. So we have to use some other identity mechanism to orchestrate the kickback, which fails in two ways:
- Either it's too disconnected from the original transaction, and there's no way for me to hold the seller accountable for the Bitcoin I was promised in exchange for a positive review (aside from buying from the shady seller a second time just for the opportunity to leave a negative review).
- Or it's too connected to the original transaction. In this case, if our side scheme is uncovered it could be used as evidence against us in court. Which is a significantly scarier outcome than being banned. Although being banned also carries more weight because some sellers won't sell to accounts without positive history, so if you need to reboot your identity you might have to risk getting ripped off a few times before the larger community of sellers trusts you again.
Also, I'd stay the hell away from any seller that approached me with such an offer, they want me to participant in a scam, which tells me something about them. Why should I trust their drugs?
But a darknet market purchase? That's different. One goes through all kinds of ridiculous gyrations to prevent third parties from being included, and with good reason. Unless you think you can compromise legit user accounts, your bots would have to spend a whole lot of money on real drugs before anybody would give credence to their fake reviews.