This randomly came up today and I got to thinking about when the price system is the best way to distribute things, I should mention that this is off the top of my head so it might not be a textbook complete answer. This is related to my other post about price gouging.
So the assumptions i’m going to talk about are going to be in order of ascending rarity: unequal utility; limited resources; limited wealth inequality; and rational people.
Unequal utility, this assumption is the easiest to meet, its hard to even think of a situation where utility is the same. This is because not everybody values things in the same way, even if its their life you are talking about, some people may be suicidal, whilst others might be willing to kill a hundred babies to live. The trick here is an element of perception of utility, one might perceive a higher or lower utility than the actual one he will get and that might distort things, but this is probably more relevant in the rational people section.
Limited resources, this is also fairly easy to assume, there’s never an infinite amount of resources. If you have an infinite amount of television sets available to people then they will maybe use the first 3 to watch 3 channels at once, maybe more if they handle more than that, then, the next couple will be for backup, then maybe you would like to use the next couple as chairs around the house, then the couple maybe for releasing stress by dropping them off the 7th floor. The point is that there is diminishing marginal utility from these televisions but since they are free you have no reason to stop getting them. Of course what matters is not whether or not the resource is infinite, but whether your access to it is infinite.
Limited wealth inequality is touched on in my last post but its also an important assumption. Relatively more money allows for relatively more leisure, if there is a heart for sale and someone only has 10 dollars and is willing to use it all to purchase this heard because his is about to expire. But someone else who is in fine shape whose heart is only 0.1% likely to fail him in the next decade but who has a trillion dollars, would maybe be willing to pay 1000 dollars to buy the heart and freeze it somewhere as insurance. Here excessive inequality has led to the item in question not being used to its highest utility.
I should mention that the wealth doesn’t have to be a liquid asset, even a house or future promises to achieve something, maybe even offering yourself up to be a sex slave, in this case even gender creates inequality, since if the vendor is a straight man, then females will have an extra option to exchange for the heart.
Rational people is in my mind the most far reaching assumption. This is because you might have people who use morals, religion, or have some other irrational mechanism with which they make decisions. There are many cases of people not adapting to their environment to offer up the service or product required to achieve their end means because of morals. You might be desperate for food and find someone selling a loaf of bread for 1000 dollars and think that he is ripping you off and so you decide to wait for someone cheaper to come along, without knowing if this cheaper vendor even exists.
Worse yet, even if there is perfect equality, and a given person x has a higher utility than everyone else and there is only a single unit of the product that will save him, and he knows that there is only one unit and only one chance to buy it(heck it could even be free), he might still decide to forego it due to religious reasons.
We must also assume rationality from the vendor’s side, although its perfectly rational to accept only cash if you don’t trust the people around you. If he does trust everyone to a good degree then he should be able to accept illiquid forms of cash as long as the time value of money is taken into account in the form of interest. It is also true that for the vendor to perfectly utilize the price system he must be able to analyze and calculate the perfect price for his product at any given time in order to make sure that he sells it at the highest price where it is going to be sold out. Even if you sell a bottle of water for 100 dollars, you would have been better off selling two for anything over 50, so its important to be able to price things as optimally as possible.