First time going to this dealership for an oil cha...

First time going to this dealership for an oil change. Gave the service rep a coupon from their dealership before he wrote up the order and he took the coupon and didn't mention any issues. When we went to pay after the service, they said that since it's a Lexus they won't honor the coupon and wanted to up-charge by about $45. It's very dishonest to say that they won't honor a coupon when they had it before writing up the work order. They finally agreed to honor the coupon after a long long discussion. We have never had such issues at the Toyota dealership in McKinney since Lexus and Toyota are the same company!! Also they charged a 3% fee for using credit card.