I like your motivation and all, but be prepared to be dissappointed. Car Audio shops don't do the business like they used to, especially with all the stuff you can get online at half the price and the constant DIYers out there. More and more this is how the car audio field is going. I would have said years ago, yes, go out and start your own business in this field, but not so much nowadays. Most of your well-known car audio business's have been around for awhile and have a customer base and what not.
I used to do customer service and helped out in the back when they needed me and this was years ago at my friends shop. It used to be boomin' back in the day, but he has closed up shop to move to a higer traffic area more the 3 times now in 5 years. He is thinking about closing up for good now. With rent in the building, not making much on custom installs, or just basic, then he won't have much of a choice.
It is really harder than most people think. There are some here like Noah and others who have gave great insight and trust me, listen to them.
edIT: I got to call audio express and hot wired car audio in jonesboro to see if they will let me have their blown used equipment( mojos/jl subs/etc).
I have decide to offer a 30day limited warranty/insurance on all my installs, anything after that is all on the customer. Unless they blow a woofer, which they shouldnt. But in the event if they do then if it were to happen after the 30 day period they will have to go through the company.
With that said, good luck and I hope it does work out for you and this other guy. Just be careful and don't get over your head before it is too late. Also stick to name brands till you make money, like Kicker, Alpine, MTX and if you can get it, JL and Memphis are good brands to have as well. Even lower end shit like Dual and Jensen will sell. We used to sell the shit out of Audiopipe and Audiobahn back in the day, lol!