Discount Muffler Brake

I went in to have a new exhaust put on my car, I supplied all the parts but I needed someone to do the work because I have no way of lifting the car on my own. I was told the work should take about an hour and at $85/hr I had no problem with the $90 estimate. It only took 30 minutes for the work to be completed but the owner/manager still wanted to charge me $90. We went back and forth for 5-10 minutes before I finally decided to pay, leave and not let this ruin my day.