We also used Sullivan Solar, and I’m a bit bummed that we went along with the string inverters vs. panels with micro-inverters (and I knew about the difference going into it, which bums me out even more). We have quite a few trees near our house/yard that shade some of the panels throughout the day. With micro-inverters, I think we’d be producing quite a bit more energy than we are with the string inverters. Just something to think about.
And Sullivan is not a discount installer, so you’re not really getting a break on the price. That being said, we went with the larger, more-established installer for the reasons stated by the OP, above. We didn’t want a fly-by-night company that would go out of business in a few years (and there goes the warranty!).
I would prefer that they NOT pay people for referrals; it taints things. We got the recommendation from a neighbor who didn’t disclose that he would be making money from the referral. Had we known that, we might have considered another company. Good companies should not have to pay for referrals — their work should stand on its own, and people should be happy to refer others because they are genuinely happy with the materials, workmanship, and follow-up from the company.