I would actually want to check the work to make sure everything was done properly. I remember one year bringing in my outboard to be winterized (I usually did it myself). I paid for the work that they said was done (felt I was over charged), which included changing a prop shaft seal. Put it on my boat in the spring and the lower end blew a month later because they didn't put oil in it. I had no way to prove it, but.........
Definitely learn to do it yourself, it's easier than you think. Went to another marina to see how much to fix, they quoted $2000, which was more than the motor was worth at the time. I looked around a little and found a lower unit for $250 and replaced the seized (I mean seized LOL) unit myself.
I don't want to offend any marine mechanics on here, but I have never had a good experience in this field. Not including all the horror stories that I have heard over the years.