I was robbed like that too.
While I had my boat in Fort Lauderdale, I arranged for the 50 hours check up of my engine with a "Volvo authorized dealer". The original bill was over $650 !@#!@!. After I complained and asked the reason why it was so expensive, they told me that 1) they had no experience with my type of engine. 2) they were charging for the hours it took them to find out and order the parts that were needed, and 3) they charged for the time it took to the mechanic to find the electrical switches on my boat!!!. ( I was in New England at a time and they did not attempt to call me). After my laud complains, the lowered the bill to $400, still a rip off for a change of oil and filters, I thought.I later found out that they should have checked the alignment of the engine with the shaft as part of the 50 hours check up but they did not. In fact, I eventually discovered that one of the engine mounts nuts was missing from factory and causing excessive vibration. I could go on and on with several bad experiences with mechanics and boat yards but suffice to say that now I do my own maintenance and repairs as much as possible. I know there might be honest people out there, but there is also a large crowd of crooks around them.