Mazda service overcharging

Are Mazda dealers deliberately charging customers for unnecessary extras when servicing their cars? Two dealers I have used recently to service my 2013 Mazda automatically added a charge for the "optional" premium motor oil. Challenged, both tried to explain it away with reasons like, best for your car, that's the only oil we stock. I reminded both this was an optional extra and customers must be asked. Both removed the charge. Additionally, one dealer attempted to charge me for tyre rotation (included service). I was advised that the rotation was free, but the charge was for wheel balancing. It was sold to me as  "essential". Strange no previous Mazda dealer had "suggested" this "essential" charge when they rotated my car's tyres. If I hadn't challenged these extras I would have incurred an additional 12.8 percent cost over my "fixed price" service charge. I suspect most customers would just go with the dealer on these. A nice little earner for the dealers.