MADISON, Wis. -

During the holidays, many shoppers turn to the web to compare prices between stores. But buyers should be wary; some stores don't have to match their online prices.

Stores like Walmart have policies that explicitly say they will not match online prices. In Wisconsin, the retailer said it's because of the Unfair Sales Act, which prohibits companies from selling below cost to undercut competition. Walmart told WISC-TV the law prohibits them from matching their online prices after a consumer came forward about overpaying for a product.

Kimberly Hazen from the Better Business Bureau said it's up to the consumer to read the fine print and make sure they're getting the best deal.

"Some of the stores seem to think that they're protected and maybe it's just a case that the consumers just haven't made a big enough stink about it," said Hazen. "Shoppers should check around. What we don't want to do is spend hours and hours and hours shopping for an item, but that's exactly what we have to do if we want to get the best price."

According to Cheapism.com, stores like Target, Sears and Best Buy all price-match their own sites. Retailers Walmart, Kohl's and J.C. Penney refuse to match their own prices.