I think the point was that it is hard for participants to cheat, the owner isn't going to go lower than a certain amount; thus, the owner is always going to break even or profit. If the owner puts the price too high then the buyer is no longer going to be a buyer, but a a person who is walking away from the deal. Kind of self-enforced because the person who is selling is not going to make money by putting too high a price on goods.

And it's easy to cheat in bartering -- just don't tell the other party that your goods have some hidden flaw.

If I barter you my old laptop that crashes when you leave it on more than an hour, you're going to be mad later when you find out I didn't tell you, and you'll have to appeal to a third party for justice if I'm bigger or stronger than you.

Bigger or stronger won't stop a bullet. Anyone who cheats in a way that seriously damages the other, in a world that has guns in it, is a f*cking idiot.

EDIT: This is known as "deterrence" if the potential malefactor is fairly bright and "evolution in action" if not.

Or just barter it away to someone else (with or without telling the truth). ;)

This depends on the perfection of market information. If both participants can perfectly determine the value of their and their adversary's goods, no one can or will cheat.

So barter should work for metals traders but not cattle traders (but they have other problems...).