Clark is a member of all three warehouse club – BJ’s Wholesale, Costco Wholesale, and Sam’s Club. But he’s particularly fond of Costco. The most any item is marked up at Costco is 14 percent. Yet, some people are convinced it’s just a gimmick. They think that the store dupes you into paying the member fee. Well, Clark now has proof that it is absolutely worth it. A study by the Economic Research Service at the U.S. Dept. of Agriculture shows that you save a substantial amount of money shopping at warehouse clubs and Wal-Mart Supercenters. The study was done over a five-year period, and, on the same quantity of an item, you will save from 5 to 20 percent. As a result, those stores represent about a third of grocery store spending these days. Alternatively, regular supermarkets use “high-low” pricing, where some items are extremely cheap and others are marked up significantly. The supermarkets tout the low, sale items in advertisements to lure you in, but they hope you’ll buy the higher-priced ones when you’re there. People feel duped and don’t go back. If you are going to shop at warehouse clubs, just try not to make impulse purchases.