As a matter of record, yes you can cancel a car warranty extension. Every time a dealership certifies one of its pre-owned vehicles, giving it an extended warranty, it costs the dealership around $400. Sometimes, during the negotiations over a vehicle, if it is a matter of $400, as long as the buyer is willing to buy the car non-certified and is willing to sign off to that fact on the purchase and sales agreement, then the car warranty extension is canceled. If you buy a longer warranty term in the business office, you still have 72 hours or buyer’s remorse time to cancel, as well.
For more info, see Extended Car Warranty Ratings: Customer Reviews