A friend of mine bought a new Range Rover, even though he ran his own garage he had to have the vehicle serviced at the Dealers to comply with the warranty at expensive labour and parts costs. One time on collecting his vehicle from their Dealership 20 odd miles away, halfway home the brakes seized up on one side rear after their "Land Rover Trained Specialist Mechanics" had serviced it, he rang them and they collected it and provided a car for him to use, a few days later he drove up to collect the "repaired" vehicle, got halfway home and the other side rear brake seized. If he had serviced it himself it would have been done correctly for just the trade price of the parts and the vehicle would not have let him down.
It doesn't matter how big or small the Dealership or garage is, it is down to the quality of people actually doing the job!
A good friend of mine whose vehicles I had serviced since 1976 bought new Toyota cars for him and his family as I was retiring and he included a servicing contract as well. He ended up with costs nearly four times mine and when Mot was due their service department was finding unnecessary work on the vehicle, which when I inspected the car for him they agreed it didn't need doing for the MOT, also they advised he had the air con radiator be replaced, he said fine it is still under warranty, suddenly they decided it would be OK to leave it!!!