Offset providers respond that, while not every cent of every dollar paid to offset carbon is converted into projects, a certain amount of overhead is necessary to ensure that carbon-reducing projects are properly planned and implemented. Just as the International Red Cross and other laudable NGOs must cover their operating costs, carbon offsetters have some unavoidable costs (such as employee salaries and payments to project monitors). Furthermore, the market for voluntary carbon offsets is becoming increasingly competitive, both on a quality and cost basis. Providers therefore have a strong incentive to demonstrate to the satisfaction of consumers that their money is being well-spent.

Proponents of offsets note that market mechanisms have been demonstrably effective in dealing with air pollution in the past. When confronted with ever-increasing levels of sulfur dioxide in the early 1990s, for example, the U.S. government created a cap-and-trade market for SO2 emissions. Emission reductions were achieved more rapidly and at much lower cost than even many advocates for the program originally anticipated. If such a market-based mechanism could reduce SO2 emissions, many argue, it is not unrealistic to expect that the market may also be able to deal with greenhouse gas emissions.