Ur gonna hate what I say next but it is the solution to all the trust issues. Monero. U can use the transaction on the blockchain to verify payments, reviews, etc.
I would suppose the instance gets a 1% cut of products sold on its platform incentivising it to be better than the other instances. U solve the adding fake reviews thing by a review requiring a transaction on the xmr blockchain u can solve the removing issue since anyone can prove that a review was removed in bad faith (obviously u want to retain the right to remove reviews with people saying awful shit).
Since everything is federated u can design it so there is 0 cost to using a different instance hence an instance acting in bad faith will lose its 1% cut and thus gives it a strong incentive to behave.
If u wanna get real creative u could do a system of federated logistics where u track items with cryptographic signatures. Each logistics actor signs for the product from the previous logistics actor until the original customer recieves the product at which point funds are released to vendor and delivery. This system would allow package tracking through a decentralised logistics systems (can assign fault for loss to the actor at fault) can allow actors to specialise for a location/route and take advantage of economies of scale.
Yeah that’s the way to do it. I run [email protected] so I’d like to think I know what I’m talking about.