I had a $10 coupon. I asked the price of the "signature" service and was quoted $36.95 plus sales tax. I agreed to a "high mileage" oil which was "on sale" for $41.95. I said "so it's $5 more" and the guys says yes. When I paid I was denied the sales price because I used a coupon, and a sketchy $1.50 "shop fee" brought the total with tax to $41.55. When I asked about it, the guy wanted to argue, and I just left.
It's only $7, but it's enough for me not to go back.