Sorry for the late reply on where we buy our boxes.
We purchase direct from the manufacturers, as well as from a couple of distributers, which allows us better flexibility with some of the hotter issues, that perhaps become allocated. One pitfall some stores find themselves into is the fact that they tend to "cherry pick" if they deal with distributers, which over the course of time, puts themselves in the position of getting allocated with some of the hotter issues. This leads to overpaying for some of the annually hotter issues such as SP and SPX from secondary markets, which could lead to non-competitive prices in their stores. For our wholesale accounts, if you purchase 3 boxes of Fleer Tradition, 3 boxes of Topps Opening Day, etc., you're going to get 3 boxes of SPX. For those that continue to pass up on the less than stellar boxes, well, their allowance for the hotter issues will be limited as well. I'm sure our distributers do likewise with us, so we buy most everything, be it good or bad.
We prefer a slight profit margin, break even, or even slight loss on some of the "dogs" we purchase, if in fact, because of these purchases, it allows us more boxes of the more in demand, high end, type boxes. Basic economics really.
Funny thing really, but we get at least one "no one has asked for product "A", so I'm going to pass" when we solicit store owners with new product. Keep that in mind when you walk into your local card store and are unable to find a pack or box of your favorite issue of cards. And they wonder why their customers are going to EBay???