If you're willing to pay good money for top flight sound and system design, I would strongly suggest working with someone who'll GARANTEE that you'll be 100% satisified with the sound, or they'll switch things out to make it right!!!
You're right, there's too much incentive for most installers to use "their brands", and tout them as "the best". I personally like to use "what's going to work best" within any given budget myself. As results are the most important.
I would also submit to you that the vast majority of installations are tainted in performance potential, simply because of "monetary incentives" and "agendas" that are involved. If you can find someone who's willing to go the extra mile to GARANTEE only the best possible performance at any given price point, I'd go with that one in a heart beat! Mediocrity is all too easy to come by, and is the norm sad to say. Mostly those guy's know about as much about getting world class sound as your average audio enthusiest sad to say. Good luck
