Former Costco employee here - nope. A lot of the point of the store is reselling large items to small companies. Not many families need gallon jugs of butter or 100lbs bags of rice, but tons of restaurants do.

That being said, the reselling is normally for people who do something with it (ie cook the food, print with the ink, etc), not turn around and sell the exact same product.

"Reselling against their membership agreement"?! Uh, not likely - I think half of the corner stores, and most of the low-end restaurants and delis, around here buy at least some of their inventory from Costco.

I'm guessing Costco's business is at least somewhat dependent on having successful resellers buy from Costco!