This is kind of like what happens internally on platforms for 3rd party sellers like eBay, Amazon, and AliExpress. Even decades later they’re still working the kinks out obviously. Amazon and AliExpress particularly have lots of scammers, so they clearly haven’t figured out the secret sauce yet. They’re not under-resourced, so either they’re under-motivated to weed it out or it’s actually pretty tricky to do.
My guess is it’s both, but more that it’s just tricky to implement a reliable system of reputation and trust. EBay and Amazon got around it early on by being cheap and establishing policies that heavily favored buyers in disputes, which made the prospect of using the service less risky to the public, improving their market shares. They probably also have non-trasparent systems for tracking buyer reputations as well to avoid abuse.
It seems to be the norm to keep these systems obscure to avoid abuse, but to make a truly functional open platform you would need to have public systems, so I’d hope that the norm of obfuscation is out of convenience or laziness and isn’t required to make the system function.
The link has a 500 error for me. Can you say more about this?