Some interesting comments about having your credit card can get flagged if you make a small purchase at a convenience outlet and then go on to make a big purchase several hours later. From a comment Cliff left:
When I worked at MBNA (now Bank Of America) the fraud department used a lot of different algorithms to detect fishy behavior on cards. The expiration date is, of course, a dead giveaway. But other indications are things like a small purchase at a gas station or convenience store followed immediately by a high-priced item. Most crooks try out the card somewhere inconspicuous, like a convenience store or gas station to make sure the card works. I guess the theory is that if the card fails it is easier to back out of a convenience store than a big purchase.
A bit of reading lead me to find out that higher gas prices and gas shortages are causing more people’s credit cards to get flagged:
Buying less than 50 cents worth of gas is a reliable sign that a stolen credit or debit card may in play. However, gasoline shortages are showing up nationwide and it may snag honest cardholders who insert their card, start the pump and then shortly discover the station’s tank is dry after it dispenses only a few cents of fuel. Fraud detection systems pick up on typical patterns such as hitting unattended payment terminals like gas stations and then shopping at electronics and jewelry stores. But, the systems cannot adjust on a dime and you may find your credit card being placed on hold due to a unintended tiny gas purchase.
If you make a small purchase at a gas station or a convenience store (whether intentional or accidental) and then are going to make a large purchase, it’s probably worthwhile to call the toll free number on your credit card to tell them so that your purchase is not denied.