Many people mistakenly assert that the worker has been unjustly deprived of $100 of what should have been his "just" wage.  He has been "exploited".  After all, if the desk was worth $500, then he should have been paid $500 for building it!

According to this view, which is often articulated by labor union organizers seeking a "just and fair" wage, every dollar of profit is an "unpaid wage", that should have gone to the worker.

But what if you as the purchaser of the desk for $400, were to sell it for $300, or a loss - $300 being $100 less than what you had paid.

In this case, you would be treated rather lightly and dismissively by the labor theorists.  You would have suffered financially and this would be regrettable of course, but almost no one would suggest that you had paid the cabinetmaker "too much" for the desk, or that the $100 you had failed to recoup in the re-sale of the desk would amount to the theft of $100 by the cabinetmaker, or that the cabinetmaker had exploited YOU, the purchaser.

From this we see clearly, that under the labor theory of value, the cost of production, selling price, and the value of the item, are all one and the same.  But this is not the complete story.