Here’s one answer you might not like: Knowing your name and ZIP code allows a retailer to easily find your entire address so they can send you lots of junk mail and also sell your address to other marketers.
Not exactly the reason you thought, eh? It seems that many people think stores use ZIP codes to figure out where customers are coming from or to confirm that you and your credit card are a match.
In fact, there are several reasons why you should say no when a store clerk asks for your ZIP code or any other personal information.
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The store’s agreement with the credit card company does not require it. CreditCards.com said:
Visa and MasterCard state in their merchant rules that if the back of the card is signed, a merchant may not make giving personal information a condition of making the sale. If the card is not signed, they may ask for identifying information. American Express requires merchants to check only the signature on the back of the card and does not require any additional identification. Discover does not prohibit a merchant from asking for such information, a spokeswoman said.