A woman looks into the window of a store advertising summer sales. Although the sales prices are printed on paper, it may be difficult to actually buy an item on sale. - 

If you're going through those weekend circulars and you happen upon a really great deal for a laptop, say, or a mattress, we have a cautionary tale for you. Getting that price may be easier said or seen than done. David Segal writes the column "The Haggler" at the New York Times. 

According to Segal, getting an item at the advertised price is sometimes a problem if you refuse to buy extras with your purchase, such as a protection plan. He talks specifically about this issue at the office supply store Staples. Customers have complained about how they'll try to buy a computer on sale, have the sales associate confirm its availability -- only to be told that the item is no longer in stock when they decline to purchase a protection plan, one of the priciest add-ons for a computer. It's called "walking the customer," trying to get that person out of the store as quickly as possible. 

Refusing a sale seems counterintuitive to a business, but Segal says it makes perfect sense when you look at the carrots and sticks Staples has for its salespeople. The company uses at a program called Market Basket, which tracks the sales of each associate. A salesperson must sell an average of $200 worth of extras every time they sell a computer. If they don't... 

"A number of sales people explained to me that if you don't keep your Marketbasket average at $200, you'll get creamed," Segal said. "You'll a lecture, you'll get probation; you'll get night shifts, weekend shifts, and if you cannot keep your numbers up over the long term, you'll get fired. So as weird as it sounds, it makes perfect sense for the sales associate."

How to avoid this problem? Segal says the best thing a customer can do is emphasize that the stor needs to honor the advertised price.

Take a listen to the audio above to learn more about this business practice.

Follow Tess Vigeland at @tessvigeland