That's why there is a user rating system. Even when a question has zero upvotes, you can still see the seller rating, which is calculated from the total history of their sales.

So if you see an answer with zero upvotes, but the user has 500k sats in total sales, and a 90% positive rating, you have a good chance that his answer will be good.

It's the same principle used for darknet markets, the seller can rug-pull you, but they will ruin their reputation.