Are You a Victim of the Costco Effect?

A new CNBC documentary explores why we always buy more than we need at the big box giant

It’s a Saturday afternoon and you’re about to make a run to Costco for the usual suspects worth buying in bulk: toilet paper, wine, toothpaste, Q-tips. An hour later, you’ve left the store with a couple of DVDs, a giant tub of salsa, a 12-pound crate of navel oranges (for your family of 4) and a Polo button down (yup, Costco sells these, too).

If you’re one of Costco’s 64 million members, chances are you’ve succumbed to the Costco Effect, the tendency to give in to discounts by spending more than you expected and buying more than you need.

I stopped buying groceries at Costco a while back because so much of it would spoil – like that huge crate of oranges. And I knew I was buying stuff – lots of stuff – that I didn’t need just because the price was right. How many times have you bought a dress on sale and never worn it?

At Costco, the temptation is multiplied because, well, you’re shopping at a warehouse that sells EVERYTHING. Literally. And there’s so much more you can buy that isn’t even on store shelves. Costco also sells cars, insurance plans, caskets, wedding dresses, diamond rings and vacation packages. My parents are looking to replace their above-ground swimming pool this summer and yup, Costco sells those too (with installation). We bought our cultured stone patio set at Costco five years ago. To this day, it rates as my best-ever warehouse store purchase.

It’s a pretty genius business model. Never advertise, charge your members and sell just about anything without ever marking it up more than 15 percent. The result? A reported $93 billion in annual sales. The world’s largest membership warehouse chain, Costco is the subject of a CNBC original documentary that premieres tonight. Hosted by CNBC’s Carl Quintanilla, the program takes a look at how Costco has grown to 600 stores by convincing people to pay for a chance to save money.

Do you shop at Costco? What’s the strangest thing you’ve ever bought there? Tell us in the comments below.

CNBC’s "The Costco Craze: Inside the Warehouse Giant" airs Saturday, April 28, and Monday, April 30, at 8 p.m. ET/PT.

Dina El Nabli is iVillage's Health & Lifestyle Editorial Director. Follow her on Twitter (@dinaelnabli).

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