I shouldn't have used vehicles since they are a special case in some states. At the federal level, taxes on barter income match my description. [0] Taxes are still zero if the company can claim the fair market value of the services they offer you equal the value of your clicks.
If you accept a trade-in on the sale of a vehicle, the allowance for the trade-in cannot be excluded from the amount on which tax is based.
For example, if you sell a car for $20,000 and accept a trade-in valued at $4,000 as partial payment, tax is based on the $20,000 selling price.
Source: http://www.boe.ca.gov/pdf/pub34.pdf