Tim, Almost any small business could learn to pay commission on work otherwise not realized that is brought in by an employee. If an employee just stands in the shop waiting for work to come in, no. If they are pro-active and open the door ten minutes early, no.
If on their time off or away from the store, they secure work that would not have normally come to the shop, why not compensate them for their initiative. They are working hard to make your store such a success that they are guarenteed an on-going job. It's call jene se qua, or "a sense of ownership" and I probably butchered the french spelling.
There are some "Wage and Hour" considerations when paying commissions and bonuses. If overtime is in play the time and a half must be paid on the regular hourly wage AND the comm.(divided by the hours in the pay period and that amt. added to reg. wage rate)