You can't. But you can trust that negative reviews are not fake.

No one would give themselves a negative review on purpose. And this is key.

I worked out these problems a few years ago, but never followed up. Both due to lack of ability and due to, y'know, enjoying being able to sleep at night without wondering whether it's my last day on this pillow.

Competitors will give someone a fake negative review... it happens all the time on Amazon

In this world the customer base is a lot smaller. If there is a question about that reviewer being unauthentic, a request to see a label, or tx block is straightforward way to weed out bad actors.

It's a lot harder to get away with fraud in a smaller customer base operation and the people who run the marketplaces are not interested in allowing fraud to persist, they also have an incentive to squash that, unlike amazon.

You’d have to choose to do business with a competitor. And that won’t happen more than once.

Or do business with any newbie on the network, who might be a competitor. Or do business with any customer who gets their account hacked.

That doesn't help much even if true. A vendor could create an account with lots of good fake reviews and a few real reviews, good or bad. They'll look the same as an established vendor with lots of good real reviews.

The other half of the equation was to make it costly to create vendor accounts. A vendor is required to send crypto to a nonexistent address (proof of burn).

That makes newcomers a juicy target for competitors to leave fake negative reviews. If you need to pony up $10000 to start a vendor account, a competitor can spend $1000 to leave 40 bad reviews, assuming $50 each and reselling at a 50% loss.

If you need a 90% positive rating to be trusted, you'll need 400 good reviews, about $20000 in turnover.

It's too cheap to ruin a vendor and too expensive to maintain one.