You wouldn't work either, if you were the Labor Theory of Value.
Just as the Libertarians have their myth that a "free market" will determine the true value of things, the Marxists have the myth of a Labor Theory of Value. Both fail because of a lack of scientific thinking (see also, Richard Carrier talking about how difficult, but possible, it is to scientifically determine true values).
But the Labor Theory of Value (LTV for short) vanishes when you look for it.
According to wikipedia, the starting point for Marx's argument was as such: "What is the common social substance of all commodities? It is labor." And yet "economic demand", "supply", exchange, and a "value chain" are also required for all commodities. Even more so: it requires no significant labor to randomly find a rare valuable stone, created entirely by nature. But it always takes demand to sell it.
That should be the end of that. But ever-increasing "epicycles" are needed to make the LTV fit the facts. Because people who struggle with scientific thinking do that sort of thing.
You will never find the value in the labor
A labor theory of value should be able to tell us what the value of something is just by looking at the labor required. But this will never work, because we can always ask "why does anyone value that labor"?
Does muscle power determine value?
Heavy lifting? Sometimes it's valuable, like when building a house. Other times, it's useless: when lifting a rock just for fun. Small movements of the hand? Highly valuable when it produces great art, or performs surgery. Useless without such a context, just exercising your finger muscles. What about sitting still? Just thinking? Good ideas can be very valuable. We'll miss you, Stephen Hawking. Then again, bad ideas, or no ideas at all, are not as valuable. Thus we can't tell by looking at the labor (especially not the "amount" of labor), we have to look at the context (see my discussion of results caused by the individual plus the context)
The non-scientific thinkers, as they do, are quick to invent an excuse: the labor has to be "economically necessary". But this concedes the point: the value is not found in the labor, it is found in the "economic necessity", which is just a fancy term for "economic demand".
Does skill determine value?
A lot of the above examples of valuable labor involve skill. So we might be tempted to make this into a "skill theory of value". Then, house builders are paid by skill, surgeons are paid by skill, and the owners are paid by skill of managing their assets. Right?
Not so fast.
Skill suffers from many of the same problems. You can train yourself to be highly skilled at something...only to find that no one cares, no one will pay you to do it (though I suspect a few misguided souls in the art world will always have your back, perhaps for ideological reasons). For example, think of the surgeon. Would anyone pay the same salary for that surgeon to use that skill on nothing but cutting fake rubber heart models all day every day? No. Once again, it's the context. The demand, and the value chain.
Does time determine value?
Apparently, lots of Marxists, possibly even Marx himself, considered time to be a crucial factor. So much so, that maybe the whole theory should have been called the "Work Hours Theory of Value". That's certainly what I will call any such theory, from now on.
This still begs the question: why are some uses of time valuable, and others are not? Oh, right, demand. Again.
The context and the demand for labor
In what context is labor/skill/time valuable? When it is in the context of a value chain. What makes this chain of labor valuable? Demand for its results. Who produced the chain? The people organizing it.
Ownership is labor
One thing a Marxist cannot have, is for a "capitalist" (read: owner) to deserve any pay whatsoever.
And yet ownership is labor. How? Because decision making is labor, and ownership is decision making.
You could ask "how much labor is it though"? But as we saw above, there is no way to look at labor to determine it's "amount" of value. It doesn't matter if the labor itself appears to be hard work or not. We have to look instead for the demand. Or, how valuable the contribution is to the result.
Isn't this all a misunderstanding?
And yet, it seems, the whole point is to use this theory to prove things like surplus value and then exploitation of labor. And that means, paying people less than what they contribute. Which means, you need some way to determine how much people contribute before you can say whether a wage is more or less than that amount. But it seems Marxists get this all backwards. They start with an assumption about what the labor is worth: it's worth all of the added value of the product. And the owner contributes zero.
But that's circular reasoning, begging the question. Does the owner really contribute zero? Is all the added value only due to the workers? You can't give the LTV as an answer to these questions if it merely assumes the answer.
It may yet turn out that the true interpretation has nothing to do with fairness, or what people should be payed. But I can't tell what else could be the point.
People value things. They want or desire this or that. They can value products, services, contexts, themselves, other people, all kinds of "things".
People can even value good jobs.
This would seem to mean that people would give up some money in exchange for a better job.
And they would demand more money to convince them to do a job they don't want to do. Like cleaning toilets or something.
Never mind that nearly everyone has the skill to clean toilets. Never mind that it isn't "as much" labor as playing hockey.
If people don't want to do something, that's value that has to be paid for.
Lastly, it is not enough for someone to want something (and be willing to pay it's dollar price) at the moment. They may buy it, and get everything they hoped for, only to find that they aren't satisfied. There is a difference between descriptive economics, and prescriptive. Even the market solution to the economic calculation problem is merely descriptive. The market tells you what people do choose to buy, and for how much. It doesn't tell you what they should choose to buy, and/or for how much.
You can be mistaken about the facts (like what the problem is, what can actually fix it). Scams are an obvious example (to this, Libertarians say "oh well, people should be free to make stupid decisions", which is a prescriptive claim I'll have to examine in another page). Maybe a product or service has side effects, like pollution, and then you have to pay to fix these side effects too. So you have to pay more than you realized. Or maybe no one would ever have bought a car if trains and bicycles had less overall cost in terms of not only deaths, but also complex effects on society we can hardly imagine.
You can also be mistaken about your own true values: what would you really do with those dollars if you were informed of all the facts and reasoning without fallacy?
Some fixes have been invented to help with this. There are 30 day money back guarantees. There are reviews, like on the Amazon website. And, of course, we can use the legal system to sue people.
For the scientific discovery of true values, see Richard Carrier's writings on the subject, for example here.