well the one thing i hope for you employees is that they are knowledgeable and not arrogant about the brands you carry.
the biggest problem i ever see is the fanboys for whichever brand claiming its the best no matter what a customer could be looking for.
For example
"I'm looking for a loud sub to use for spl"
dumbass: Buy a W7
"I'm looking for a good sub for sq"
dumbass: Buy a W7
Make sure they at least have a diverse view of the car audio world, or are willing to learn at least. The more knowledge they have, will help your business a lot. You don't want to gain a reputation based on your employees being idiots about the equipment you carry.