The existence of this prohibition DOES change the behavior of the seller -- he no longer spends his time standing in the middle of the desert with a glass of water.
There are several ways in which the behavior of the seller changes. Some may benefit the buyer (as in your anti-gouging example) but some may not (such as if the guy with the glass of water would have had one anyway). Furthermore, there is no reason to believe that the benefit you describe happens only at the market price; it may be that people in the area are willing to pay 50 times the normal price for lumber, but 20 times is sufficient to incentivize you to truck in a load of lumber.
here is no reason to believe that the benefit you describe happens only at the market price
Sigh. Why do you think central planning failed?
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
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