One insight often ignored in the debates about price theory is something that businessmen are keenly aware of: in different markets, prices may not function according to the same principles except in some very abstract (and therefore not very useful) sense. From the classical political economists to Michal Kalecki it was known that prices for industrial goods behaved differently from prices for agricultural goods, but this idea could be extended further to other broad classes of goods and services. Marxists assert that value derives from the volume of socially necessary labour time exerted in the creation of an object. This value does not relate to price in a simple manner, and the difficulty of the conversion of the mass of values into the actual prices is known as the transformation problem. However, many recent Marxists deny that any problem exists. Marx was not concerned with proving that prices derive from values. In fact, he admonished the other classical political economists (like Ricardo and Smith) for trying to make this proof. Rather, for Marx, price equals the cost of production (capital-cost and labor-costs) plus the average rate of profit. So if the average rate of profit (return on capital investment) is 22% then prices would reflect cost-of-production plus 22%. The perception that there is a transformation problem in Marx stems from the injection of Walrasian equilibrium theory into Marxism where there is no such thing as equilibrium. Price is commonly confused with the notion of cost of production, as in "I paid a high cost for buying my new plasma television"; but technically these are different concepts. Price is what a buyer pays to acquire products from a seller. Cost of production concerns the seller's expenses (e.g., manufacturing expense) in producing the product being exchanged with a buyer. For marketing organizations seeking to make a profit, the hope is that price will exceed cost of production so that the organization can see financial gain from the transaction. Finally, while pricing is a topic central to a company's profitability, pricing decisions are not limited to for-profit companies. The behavior of non-profit organizations, such as charities, educational institutions and industry trade groups, also involve setting prices. For instance, charities seeking to raise money may set different "target" levels for donations that reward donors with increases in status (e.g., name in newsletter), gifts or other benefits; likewise educational and cultural nonprofits often price seats for events in theatres, auditoriums and stadiums. Furthermore, while nonprofit organizations may not earn a "profit", by definition, it is the case that many nonprofits may desire to maximize "net revenue"—total revenue less total cost—for various programs and activities, such as selling seats to theatrical and cultural performances.