Mercedes-Benz of Plano

I put my car in for routine 10,000 mile service for my GL 550. I got a phone call from service advisor saying that tire pressure monitor is reading low pressure and he found a nail in my rear passenger tire. He said it would cost $500 and some change to replace it. I suspected something is not right since I had no tire pressure warning when I dropped off my car. Since I usually use Discount Tires, I told him I will take my car to Discount Tires for that. When I picked up my car, the service advisor did not even meet up with me. I asked for service manager who cannot find the nail as he and I inspected the tire together. I drove my car for another 7 days, and tire pressure monitor is still not showing low pressure. Tire pressure for all four tires are good. It seems that the service department tried to scam me for a tire that is over $500. The cost for the services at Mercedes dealership is higher than non-dealership already. Why trying to charge customer for unnecessary services??? In addition, I scheduled an appointment, but had to wait for 30 min before someone came to talk to us. They were helping people who came after me. That's not right. Service advisor was acting like he was doing me a favor. Completely rude! I did not expect this kind of service, or the lack of service, from Mercedes Benz. Unbelievable. I can't comprehend how Mercedes Benz would allow their authorized dealership to treat their customer in such manner. RUDE, DISHONEST, DECEPTIVE, UNPROFESSIONAL!!! I lost my trust in Mercedes Benz of Plano. I will not come back to this dealership since I cannot trust what they tell me anymore. Beware of Mercedes Benz of Plano!