If you want an inspection, then you should pay for it. If it doesn't check out then yes you'll have to eat the cost of the inspection but you won't eat the cost of the boat. It is your insurance policy so why shouldn't you pay for it. Also, there would be many variables such as maybe the numbers are borderline, who would pay then? You should do your own inspection first and decide if you want it and only then pay for a mechanic to check it. If you are not familiar with boats, take a knowledgeable person with you if possible. Even after an inspection is it somewhat of a [censored] shoot.
When you are looking at boats away from your area you'll just have to call and find a mechanic in that area.