There are some allowable merchant practices that may appear to be in violation of credit card rules but are just not widely known. For instance, although adding fees and surcharges to a credit card purchase is in violation of credit card issuer practices, a vendor is allowed to add a convenience fee for specific transactions types. For example, if you are paying your telephone bill at your local sandwich shop -- a service that shop offers, but a business outside of that shop's routine practice -- the shop can charge a convenience fee for processing the utility payment for you. Some other rules are tricky; here are the most common examples:

The good guys

Most merchants operate within credit card issuer rules and are aware of what can and cannot be done, though the maze of regulations can be confusing. For example, Cheryl Lavenhar, owner of Knit -- a shop geared to all things knitting --  in Roslyn, N.Y., warns, "It's illegal to say you don't take a card if you do." Lavenhar also points out, "And you cannot charge for the use of that card." However, those violations aren't technically illegal, though consumers can and should report merchant violations to their credit card companies.

Merchants have a choice

"Although my business needs mostly involve check and cash payments, offering charge cards is a useful tool that helps my business and keeps the economy moving," says Denise Wolfe of Stage Design Interiors Inc. of Locust Valley, N.Y., a company that stages homes for sale. Wolfe adds, "I'm happy to be able to allow customers to have a choice. It's more profitable for me to offer the charge and to stay within the rules of the credit card companies."

Wine and Spirits in Commack, N.Y., agree to the terms because credit cards are an important payment option for their businesses. Owner Mark Zias says, "Half of our customers use credit cards these days, and purchases here can be expensive. We have to offer the option of credit. I'm not crazy about the transaction fees and percentages, but we do everything by the book here."

Consumer alternatives

Naturally, inappropriate merchant behavior is frowned upon and an American Express customer service representative explains that its merchants pay for the service of accepting American Express from their customers, "If a customer suspects he or she has been treated unethically, they should contact us. "Meanwhile," according to Visa, "if cardholders have any questions about Visa's rules, they should call the number on the back of their card or visit our Web site for more information." 

For relatively minor transgressions, such as "minimum $5 payment" signs, the other alternatives are to go ahead and buy another soda to bring the purchase price up over the minimum or decline to do the transaction. After all, the fees the merchants are substantial: According to the Merchants Payment Coalition, a retailing group that is fighting to lower interchange fees, they amount to $2 of every $100 spent on credit cards. On thin-margin businesses, small purchases made by credit cards are unprofitable.

"The challenge lies in how to educate consumers that the interchange fees on small purchases made on credit cards is equivalent to stealing the product from retailers -- there is no profit left," says Jeff Lenard, vice president of communications for the National Association of Convenience Stores. "The PIN debt card is less expensive for retailers to process," he says.

Lenard recalls that stating minimum charges on restaurant menus used to be standard operating procedure. "A lot of consumers didn't understand exactly why there was a minimum, but they accepted that. With the increased push to use credit cards for purchases both large and small, the interchange fees are eating up small business profits," he says.