The GAO reviewed the noncash donation programs (for example, vehicle donation programs) of 4,300 charities. It also examined the terms of 54 specific vehicle donations, and found that in two-thirds of those cases, charities received 5 percent or less of the value that donors had claimed on their tax returns.

The GAO hastened to add that the discrepancy between the amounts claimed by the donors and the proceeds actually received by the charities could be partially explained by the fact that the vehicles were usually sold at auction at wholesale prices, and the proceeds were reduced by vehicle processing fees and other costs.

Even so, the GAO recommended that the IRS reassess its own methods for determining if taxpayers have overstated the value of their noncash charitable deductions.