If your going to install 3 or 4 a week then go for the credibility. If your installing that many a week believe me those greedy generator manufacturers will hunt you down and support what your needs are. (hookers, booze, IM's to congressional pages)
What you need to do is find your market first. Use your installation skills to hone in a number that is attractive and yet cost effective. About that time the guy you are using to install those generators will quit and you will need to train new help. Back to the real world, who needs that many generators? In Florida, where we haven't had a hurricane yet and all the insurance companies are going belly up from last years storm season, generator sizing rules are next to impossible to meet to just put a standby unit in and not something that will power the whole block. (A camel is a horse designed by committee) Sell to those that need one and let the other panicked potential customers go by the wayside. It will make for better Karma.