An automotive repair facility may not charge a customer for repairs not originally authorized or requested by the customer, or a person the auto repair facility reasonably believes is acting on the customer's behalf, unless the automotive repair facility receives written or oral permission from the customer in conformance with this chapter. To the extent a charge does not exceed an estimate by 20% or $50, whichever is less, no cause of action pursuant to § 4909A(c) of this title shall accrue. Nothing in this section shall preclude enforcement pursuant to § 4903A(b)(6) and (10) of this title.