A $5 stapler topped the list of office supplies ordered by my friend Shannon. But she crossed the item from her shopping list when a sales clerk produced a $30 stapler as a substitute for the cheaper item, which had sold out.

Low inventories for advertised items and other sales gimmicks bother Charlene Haugsven, a blogger with myfrugaladventures.blogspot.com.

"Free-after-rebate items advertised at office supply stores are often sold out the same day the ad hits," Haugsven said. "Obviously the inventory levels on these items are incredibly low."

Her strategy: Visit a store on the first day of an advertised sale, and always call the store to check on supply levels before wasting gas and time.

"Once you're in a store, they try to extract as much money as possible," said Barry Boone, the CEO of CurrentCodes.com, an online site that tracks sales promotions and coupons.

Boone offers this list of sales tricks used by standard and online vendors:

Circular logic — Full-priced items are often inserted in to the mix of weekly promotions and discounts featured in store fliers. With this strategy, stores create a false sense of one-week-only urgency.

Color-coded deception — Bright signs and stickers in different colors are often used to promote weekly sales. But eye-catching signage for full-priced merchandise is also used to catch the attention of impulse shoppers. Vendors hope that a "grab-and-go" shopping attitude will bypass logic, research and value comparisons.

Hidden fees — Online specials may be touted at super low rates. But hidden fees, including lofty shipping and handling charges, can inflate shopping totals. Other strategies, including purchase minimums, can prompt you to overspend in order to qualify for bonuses, future specials or free shipping

"That's a hidden way of getting the (profit) margins back," Boone said.

Sharon Harvey Rosenberg, McClatchy-Tribune