Is it a good idea to limit a customer's credit card so that it can only be used on one user account? The user can have as many credit cards associated with their account as they like, but they cannot use the same credit card on a different account.
The idea is to reduce fraud. However, is this a meaningful concern? Would this move be an inconvenience to a customer who forgot his credit card and wants to borrow his friend's for a purchase? Is it the job of the merchant to build their own layer of protection against fraud, or should the merchant rely on the payment processor's own filters to protect customers?
This question might be better off on WebApps, but let know what you guys (and gals) think!
From a user experience perspective, I would be frustrated with this restriction. My wife and I share the same credit card accounts and have different user accounts on sites like Amazon for example. I have often purchased things for friends in exchange for cash because they didn't have a card or the credit available. It is a good idea, but in practice could be frustrating.
From a user point of view, I still have friends who are scared of using their credit cards online; I usually more than gladly offer my credit card details because I get reward points on my card, so for example on Apple's site my credit card has been used by four different users. Had the restriction existed, the merchant probably wouldn't have had the same amount of sales. It's not major volumes of sales but I'm sure you'd want every sale you can get.
Plus, in reality fraud cases would be someone having someone else's credit card details. As long as one fraudulent purchase passes, I don't think the thief would care to create multiple accounts; the first one is probably fake anyway.
User restrictions usually lead to frustrated customers, which translates into lost sales.
If you have experienced fraudulent orders from customers using multiple accounts with the same credit card, flag those orders and manually verify their authenticity before processing. You do not need to bother your customers with the details.
In addition, fraudsters usually have multiple credit cards. If you do not let them use one number, they will use a different card. It is better to let them place the order, and then determine the risk.
Implementing these sorts of restrictions do not get you very much protection - but they might inconvenience your users.
The legal standard for financial issues like these (fraud, abuse) is (usually) the reasonable person test (various names by jurisdiction), and the turn your minds to the issue test (again, various names). This supports acting in good faith, which (generally) satisfies the lower burden of proof.
As others have said, limiting credit cards to a single account would severely restrict family usage/accounts.
In addition to family accounts, you'll be missing out on large business accounts. Your product might not appeal to a business, but if it does? You'd better be prepared to accept the same corporate card for many, many users.
The responsibility of the merchant to prevent fraud does not extend to unreasonable verification methods. Check with your payment processor to see what verification methods are required.