In addition to the mechanisms from the original post,

Reputation develops over time and is why known brands can charge a premium.

You don't have to deal with scammers directly, if there's very little profit available to them. If you want to take a chance on something that seems like a great bargain, you're taking on the increased risk of being scammed.

You might even sign up with a third party service that enforces financial agreements by making merchants put down a deposit that could potentially cover customer losses from fraud. I'm sure clever people could think up all sorts of contractual arrangements of this sort.

As with so many "How would libertarians deal with ____?" questions, I want to point out that it's being raised in a statist reality where the thing is currently a problem.