With all respect labatt, your business appears to be different than most retail businesses dealing with the non-commercial market. As you're experiencing in Lauderdale, a goodly number of us are reticent to install equipment purchased elsewhere lest it bite us in the rear. We have relationships with distributors and manufacturers that we rely upon, not only for profit but for warranty and back-up when there is a problem.
The example of frying something is an apt one. (I say that, having just cooked off a $3000 submersible motor based upon customer assurances that his electrician had the proper 3 phase overloads in place!) If I'm the Furuno dealer with a ton of experience installing Furuno radars and I take on your Raytheon radar project, a brand I do not deal in, and the unit is either defective or cooks off during install, what assurances do I have that Raytheon will honor my professional experience and warranty the unit? Now my Furuno distributor knows me and knows I've put a couple hundred units in, so he's going to ship me one out overnight based upon my past performance. Most boat owners are not going to be as willing to sign a waiver as you are, either.
A good part of the money made by these guys, usually equal to the labor, is in the sale of the gear itself.
Again, I'm not trying to hammer you in any way and I'd be lying if I said that we have not, nor do not, install other's equipment on occasion, but we're always half a step away from implementing such a policy. When we do install customer supplied equipment, we do so at our normal labor rate and so, we lose our normal profit margin on the job. To charge an appropriate price to maintain our business model's profit range, I'd have to charge the amount of profit I'd have made on the equipment sale. Then where are your savings of buying elsewhere? Of course, most people don't want to pay above average labor rates to install the equipment purchased elsewhere. I've expressed frustration at similar experiences such as your's but the years have made clear to me why some outfits have such a policy.
And, from your standpoint, my experience has been that you never want someone working on a job they really didn't want in the first place. They're not properly motivated and, in my experience, someone who is turning down work is sending you a subliminal signal that they don't want the job and you maybe shouldn't want them either. I can't quantify that for you but I've experienced it. (A guy took the center right out of a $500 alloy tire rim and just gave me the, see, I told you so, look! I didn't really realize it but, he done his best to inform me that he was incompetent.)
Good luck to you and continued smooth sailing.
“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.