I actually haven’t done a great amount of research or thinking about this, but If you subscribe to a title transfer theory of contracts, then, when you transfer title to property you own (say, 50 lbs of apples) in exchange for a transfer of title to property from someone else (say, 5 grams of gold), then you are owed 5 grams of gold. If you were given a diluted coin that only contained 1 gram of gold, you are still owed the other 4, as title for 5 grams was transferred to you. So there is at least a matter of you getting what you paid for…which a private court could rule on.
Obviously there’s no real way to predict, but one guess is, in a free society, venders might have something like a free-standing performance bond, valid for each transaction…a contract that basically says “If I do not meet condition X at such and such a date, I hereby transfer as of the date the following sum _____, to ____.” That would make customers feel more confident in patronizing that vendor. Again, I haven’t given it much thought, but there’s no telling what the market would come up with…what would make customers feel safe, and what would be profitable for merchants. That’s the amazing part…if left to their own devices, people are nothing if not innovative.
A good start to thinking in these terms would be Rothbard’s chapter…
“Property Rights and the Theory of Contracts”
:EDIT:
Another option might be “consumer insurance”, which might be sold by private firms, or even by the merchant himself. There’s a myriad of “if, then” terms that could be set up in that kind of arrangement. And that’s the great part…everyone would be constantly competing to offer the best deal. And then on top of that, you’ve got their inherent interest in having a good repuation. Brand loyalty is so huge, yet people don’t even think about it. They themselves make decisions every single day determined (many times entirely) by their feelings/confidence about a certain institution. But the minute you start talking about a free market, it all becomes “oh yeah, and what about when the big guy drops his prices and then jacks them up again after all the competitors are gone?”