>While other retailers try to get me to buy more stuffs, Costco try to make sure I'm satisfied enough that I'll renew my yearly membership (their main profit source). The incentive structure aligns very well.

This doesn't make any sense. Costco makes a profit on the goods sold as well. They have every incentive to sell you as much stuff as possible. That's why they also engage in the usual retail tactics to increase sales, like having the essentials all the way in the back of the store, and putting the high margin items (electronics and jewelry) in the front. They might practice a more cuddlier form of capitalism than dollar general, but they're still a for profit retail business.