I had the same experience today with the same tech as the previous review.
Provided coupon 17.99
Was charged $21.
I asked how that could be...
They charge $1 to use Debit credit and did not use the coupon.
After 2 calls, the tech pull out $2 from his wallet. Acted like I was steeling from him.
No comments, no apologies for the over charge, no thanks for the business.
I took my next car of the day to Jiffy Smog.