It is indeed a strange thing...
My buddy has a pizza shop yet he drives a very high end Mercedes. Should I stop buying pizza from him?

How do you know where the money came from to buy the car? How do you know it is even his car?
Even if it came solely from his audio business, why should that bother you or stop you from shopping there? I doubt he is charging more than other B&M places for the lines he carries. If he is succesful, he is obviously charging what the market will bear.
Not shopping there because you don't perceive the same value as when buying used, from online retailers, other dealers, etc... seems quite valid.
Not shopping there because he "potentially" (since you don't even really know for sure) owns an expensive car doesn't make any sense to me.
Do you apply this logic to all business you would possibly transact with? If not, why the bias against the audio dealer?
George