This post is one in a series on prominent company nicknames. See all 25, and share your thoughts and memories about the $100 store below in the comments.

You know you do it. You walked into Costco (NASDAQ: COST) to save some money on one thing -- just one little thing. In our minds, we do all sorts of calculations. We see ourselves saving money instead of what we're actually doing, spending money. An hour later we walk out loaded down with bulk bargains -- and $100 lighter. That's where Costco gets its increasingly popular nickname: The $100 Store.

Bloggers and consumers have been using the unflattering "$100 store" nickname for a while. And, it turns out they are right. A recent Christian Science Monitor story cites a statistic from the Food Institute: the average visit to a warehouse club costs $93.

The $100 spending phenomena may be a universal phenomena in any of the big-box discounters. But one Harvard professor thinks the membership fees at Costco (and other warehouse clubs) make us think we're getting a better deal than we are. Michael I. Norton, an assistant professor in the Marketing unit at Harvard Business School, says that the presence of fees make people think they're getting a special discount and then they spend more.

"The presence of fees can drive choice of retail outlets, such that stores with membership fees are more popular even when they offer the same goods at the same prices as stores without fees," Norton writes in his working paper. Maybe that idea of paying to shop somewhere was crazy after all.

Frequent warehouse club shoppers can spot the newbies in an instant. With expressions of glee on their faces, they stop at every aisle. Cereal, pasta, bathing suits and batteries all go willy-nilly in the cart. Shopping lists are soon abandoned as gallon-sized containers of gourmet jelly beans along with a new iPod or DVD player find their way into the cart.

Veterans shudder, thinking of the shock and horror those first-timers will no doubt feel when they confront a $300-or-worse bill at check-out.

Clearly, warehouse club shoppers are getting wise to the best way to shop these bargain meccas. Learn some of their secrets: See, The Top Five Worst Warehouse Club Buys.