Yea it's a tricky problem, chicken and egg factor, also there's no real consensus around an identity layer on which to build one.

Amazon is a great example of botted reviews, but it mostly works only due to the nature of fiat being reversible so Amazon is a defacto escrow.

Anything new based on Bitcoin you're inherently outsourcing reputation to the centralized entity running the marketplace, so I think bonding will be a factor, otherwise without KYC where does the coordinator inherit reputation from?

WoT relays to deal with spam on Nostr are a signal IMO, if Nostr can get a little more traction as an identity layer it provides something to built a WoT and therefore reputation systems out of.