Most people think that the consumer has the right to cancel a car purchase agreement within three days from signing the agreement. This in not true. You cannot cancel a contract, but there are a few exceptions.
The dealer permits you to cancel the contract within a certain period of time. This is true for some of the manufacturer-certified used car programs or even the internal dealer policy.
The car is delivered on a condition agreement before financing is approved. You have the right to get out of the deal.
On lease vehicles you have one business day to cancel unless you waive this as part of the negotiations. This is usually in fine print at the bottom of the lease agreement.