Well, going against the tide, as is my pattern, I first want to congratulate you for this thread, Sounds_real_audio. And, also to thank you.
I believe it is an excellent step you are taking. I have little insight into you beyond what I have seen here. But, I can say, any dealer who has the openmindedness to approach the audio public with this type of query is the kind of dealer I wish to do business with. In my opinion, one lesson many a dealer would do well to learn is that there is a reason we were given two ears, yet only one mouth. Listening is a far more important skill than most realize.
Beyond that, a person who has the courage to step forward and pursue his dream deserves my admiration. Most of the people I meet are not happy in what they do for a living. We can all relate to trying to do what they love for work. It is to be congratulated, not denigrated.
By opening yourself up, and seeing what the audio world WANTS to purchase, you give yourself a better chance of meeting those needs. And, a business who serves its customers has a far greater opportunity for success than one which does not.
For what it's worth, I can tell you that the dealer has much leeway in the brands they carry. Most high end manufacturers wish to expand their dealer network, so you are mostly in the driver's seat. For the most part, you can choose the brands you carry, as opposed to they choosing you.
As to which you carry, I would rely on your own intuition - sonically, economically, and relationshipwise. It seems obvious, but selling a brand you don't believe in will not allow you to put your full energy into the endeavor. There is a lot of good gear produced by bad companies, and a lot of bad gear produces by good companies. It takes time to develop the relationship, but finding good gear from good companies should be your end goal. What I can say beyond that is to also follow the market on some level. Levinson and Krell made a lot of sense in 1988. Solid state muscle was the rule of the day, and demanding speakers dictated that. The pendulum has swung to the opposite pole over the past decade, and it seems lower power tube and boutique gear is in vogue. Still, keeping somewhat of an eye as to what lies ahead will prevent you from falling behind the trends. Finally, the setups you put together should be synergistic and sonically fufilling. Disappointment during the audition has proven to me to lose a dealer any opportunity for business. Good sound makes people happy, whether the bass is powerful or not. Since 85% of the music resides in the midrange, if that isn't very good, the chances of painting a good picture seem poor.
We all have our horror stories about nose in the air dealers who try to talk to us as if they know all and we know nothing. Should we not welcome a person who seems to be cut from a different cloth? Hey, this is an opportunity to cultivate the kind of dealership most of us want to have in this field. Let's not squander that. Little is gained by cheap shots in this instance.