Myth No. 6: Retailers can set a minimum amount you can charge on a credit card when you buy something from them.
The Logic: In a small store or restaurant, it's not uncommon to find a sign that says, "$5 minimum for credit card purchases." If this wasn't allowed by the credit card companies, surely they'd crack down on it.
The Reality:
Retailers who set minimum charges are breaking their agreements with the card companies 
. Because retailers pay interchange fees -- which vary, but average about 2 percent of the sale -- plus possible transaction fees on each credit card purchase, it's easy to see why a store owner would want to discourage lots of small credit card sales. But when they do so, they risk losing their ability to accept cards. "You're allowed to charge any amount on your card, even a penny," says Zeichner. "The problem is that the retailer wants you to charge enough to make it worth his while."
If you need to use a card for a small transaction that's against store policy, you can object, although you may be invited to take your business elsewhere. The other thing to do is contact the credit card company. "We want to know about retailers who do this," says Matt Towson, a spokesman for Discover Financial Services. "It violates our contract with them."
