I try to do it all myself. I'm pretty good with tools, my hands etc. I once hired out a bottom
paint at a local marina. They did a suck job, loose
paint still left on the boat and just pasted a new coat on top. But they didn't charge a penny more than estimated. I then had them do my power boat's bottom and the job came in at 500 bucks more becuase they had to grind out the barnacles they had not seen, fair enough.
I bring in experts that allow me to watch when I don't know how to do it. I also only use bonded, insured businesses for issues that involve safety, and I include heavy electrical wiring in that; do it wrong and the boat burns or someone gets hurt. The contractor that installed my electical add-ons last year did the job as estimated, a couple of hours late (my fault probably as I was on board watching and talking to him).
In short, I've never had a problem that I would call a problem.
I know I drip
varnish, miss spots and make mistakes. I see and feel every run, drip and fish eye I lay down, even when you don't see it I know it's there.
'Professional' just means you get paid to do it, it doesn't imbue some demi-god like ability to be mistake free. It doesn't even mean the pro is more knowledgeable about the job although with a specialist it should.
I do expect a certain level of efficiency from a 'professional' simply because they do the work more often and know the tricks of the trade.
Enlightened amatuers who love to work on boats (I'm one) do a better job, or at least try to, and when it's our boat or even a friends we do the best we can. I actually have more experience helping friends grind / sand /
paint etc.. on their boat than I do on mine.
Now if you'll pardon me, I've got some fish eyes to fix in my interior
varnish. I forgot to clean the teak with acetone before laying a unthinned first coat
