As some one has already pointed out - it comes down to how busy store #2 is.... Can she make a hell of a lot more at store #2? Yes... Can she make a hell of a lot less at store #2? Yes...

What I would suggest is that she or you or one of her friends go to the store randomly over the next day or two - different hours of it being open - 9AM, noon, 2:30, 4:15, 7... and see how many customers are there, and more importantly how many are pulling out cash or credit cards at the register - and if possible try to figure out what the average sale is per customer...

Another thing your wife can do is to call the person she interviewed back and say, I really would love the opportunity to work for you and I would love the opportunity to work at XYZ... but I am wondering, can you give me an idea of what the average sale per day a whatever the title she will have - does? I am new to concept of commissions and I just want to make sure that I have the opportunity to make more than another offer I have that has a higher base.