I've thought of doing the same thing...well not exactly but the service part, maybe spring time getting ready and such...ie...lower unit change, check and replace plugs, decarb, water pump replacements and such...but you have to watch joe q. public. They can and will stick it to you at some point. I've had so many tell me to stay away from it because of the wrong person trying to come back on you for something that you really didn't have anything to do with...ecspecially in a day and age of lawsuits running rampent.
Don't get me wrong, I'm not trying to discourage you...just some food4thot. I think it would be great myself. I just do things for friends and the such now. Normally for a good dinner or some mountain dew or something, really whatever they want. I like working on stuff and visiting with people so its all good. I do have a ranger in the shop right now I'm wetsanding for one of my students parents...lol. Its break time right now. :D
I think outfitting boats though would be an great deal. I think I would stay away from the service part though...outboard wise. To many unseens and unknowns that can come back to haunt you, and being a 1 person deal and probably using your own funds and not being a "shop" or "dealer" or whatever you could take a hard hit that would be hard to come out of. I would outfit and build boats for folks though. I really enjoy the redoing of old fiberglass boats...its amazing to see the old gel come back to life! Just my .02 cents. Let us know how it goes!
"But if serving the Lord seems undesirable to you, then choose for yourselves this day whom you will serve, whether the gods your ancestors served beyond the Euphrates, or the gods of the Amorites, in whose land you are living. But as for me and my household, we will serve the Lord.” Joshua 25:15