[thiagoharry]

No, what people will pay for the product in a market it's the price. Marx talks about the "value", which is different than price. The price is equal the value only in very limited and simplified models. Offer and demand will change the price, but not the value, for example.

What is the "value"? Well, the prices cannot be explained only in terms of offer and demand (a society with an offer of 100 pens and demand for 100 pens and offer of 100 planes and demand for 100 planes still would not sell pens and planes for the same price) nor entirely because of the price of raw materials (because this only postpones the explanation: from where came the price of the raw materials?). It also cannot be explained only based on subjectivity, because there exists a number, which is a very objective measure, representing the price if you balance offer, demand, assume competition and discard several perturbations. The "value" tries to explain this basis value that later will became the price and show objectively and numerically how the wealth is produced and distributed.

This "value" is measured by Marx as the quantity of labor socially necessary to produce the product. Given a car, the value represented by a car can be measured by the mean time necessary for the workers to produce that car in the industry plus the value transferred by the machines and tools used by those workers (whose value came from the workers that produced these machines and tools). Both manual and intellectual work need to be taken into account and you can also assume that some complex tasks or more intense work can produce more value than simple tasks in the same time.

Given this, you can compare the value produced by a worker with the value of the things that the worker can buy with its salary. This is how Marx measures these things and shows the exploitation in the society.