I don't have my own brick & mortar establishment, but my wife and I do run our own "business" within a business.
I would say be fair, be honest, and be diligent.
If you do those 3, people will notice and God will honor your business, and you should see growth (Lord willing). My wife and I are always getting business from referrals, simply because we work very hard for our customers.
I will say though, when I first started, I had a real hard time adding enough markup to really make a profit. I felt "do unto others as you would have them do to you" meant giving them the best pricing - but that would actually starve myself and my home. Since then, I just charge what I'm worth, stay competitive with my market as far as pricing, and don't take advantage of people who are in troubled times. I also am sensitive to the Lord, if I feel he wants me to give someone a deep discount, then I pray about it, then just give up however much of my own mark up to them as a gift in Jesus name, and am able to do so cheerfully. I also usually give big discounts to brothers in the Lord (those I know are brothers, not those who go to church).
The Lord did have to help me to see that making a profit is not a sin - your time, talent, and skills are worth something, and you have the right to live off of that.
Anyway, sorry there's not more scripture here - this is just the working out of my own personal wrestlings on this issue.