Never had a service and MoT done at the same dealer - its an invitation to create work and since much of the MoT fail decisions are marginal., thats easy to do.
Always have a quote for the service beforehand.
But the motor trade is no worse than plumbing or leccy work and a damn sight more honest than builders. In my experience of course
It was on it's last year of a service plan. Shot themselves in the foot as I was about to renew it.