Getting the best price is a constant challenge, and deal hunters who discover they've overpaid may have more recourse than they realize.
It's not unusual for the price at checkout to be different than that on the shelf tag. Last year, North Carolina's Department of Agriculture and Consumer Services fined six local retailers, including outposts of Walgreens, Dollar General, Advance Auto Parts and Walmart, among others, for failing price-check accuracy inspections. In June, Whole Foods agreed to pay an $800,000 settlement after a yearlong California investigation found it was charging more than the advertised price on some items.
Whole Foods, in an open letter to its customers, said its pricing during the period in question was almost 99 percent accurate. "We go to great lengths to ensure our pricing is accurate, and we corrected these pricing mistakes as soon as we learned of them," a spokesman told CNBC.
Stores typically aren't trying to pull a fast one for illicit profit. "There's just so many moving parts, so many products and sales, that it's hard to keep up with," said Teri Gault, founder of TheGroceryGame.com.
Shoppers' best recourse is to point out the discrepancy at the register before paying, but even after the fact, there's usually plenty that can be done about an overcharge. Or even the possibly more annoying price drop shortly after purchase.
A refresher on store policy and state law can yield results. Chains including Publix, Safeway and Harris Teeter have policies offering shoppers some overcharged products for free, said Gault. State laws may also entitle you to more than the difference between the correct and charged price. Michigan, for example, tacks on a bonus of up to 10 times the difference—a minimum of $1 and a maximum of $5.
There can also be recourse from your credit card issuer. The Fair Credit Billing Act gives cardholders the ability to dispute recent charges, including those in the wrong amount (say, if a restaurant inadvertently turned the $46 tab into a $460 one).
Several issuers, including Discover, Citibank and MasterCard, also let users file for a price adjustment if they spot a better deal on that item within a set period—although limitations on the number of claims each year make this a better option on pricier purchases.
—By CNBC's Kelli B. Grant