It's not uncommon for companies to have some kind of rewards system that lets you turn purchases into redeemable points, but these systems are (usually) carefully constructed so that the companies offering them come out on top, no matter the benefit to the customer. It only makes sense. Offer a decent discount and people will buy a thing. Having a point system is just an extra fun step.
But sometimes these kinds of promotions are accidentally designed with fatal flaws, just waiting for smartasses like this guy to see the cracks in the system, and grow something beautiful out of it like a proud dandelion sprouting from the sidewalk. It was done to great affect by one guy in 1999 who racked up 1 million airmiles by buying 25 cent chocolate pudding cups, and this kind of thing feels like a decent spiritual successor. In this case, it was cookies. Cases of cookies.
Maybe this dude isn't the only reason Sears went out of business, but this couldn't have helped. Here are a few more great stupid loopholes that worked.