Yes, but you may not realize it until you've been through it.
What do you charge for an hor of work? If you bill $20/hr, can you write something as complete as DotNetCart in 15 hours? If not, you're losing money just trying. Yes, you'll gain some experience, but you can gain experience and not kill yourself at the same time.
There are several levels of verification. The first is fairly simple, and that's simply verifying that the card number is valid. This is different from verifying the account is valid. You can validate a card number by checking the first digit (AmEx=3, Visa=4, MC=5, Disc=6), and length (AmEx=15, all others=16), and that the numbers pass a Mod-10 check (Google that one). For a good overview of this whole process, check out the great Bipin's article at http://www.dotnetbips.com/displayarticle.aspx?id=269. Remember that some people will enter a card number as xxxx-xxxx-xxxx-xxxx. and some as xxxx xxxx xxxx xxxx, and neither spaces nor dashes should be a part of the Mod 10 equation, so you'll have to account for that.
You also need to verify that the card has not expired.
One you get this done, you still need to verify that the account is valid, and that the transaction can be processed. For this, you need a processor account. Processors include PayPal, Wells Fargo, WorldPay, etc. There are many, and each has their own way of doing things. You pass transaction details to the processor, who verifies the account and processes the transaction. Don't forget to get the CVV, but you can't store that number in your DB.
Once the transaction is processed, you'll receive return codes indicating whether the transaction was accepted or declined and why. You'll need to notify your user one way or the other, and finish the sale, or let your user try again, or cancel the sale.
Then, by the time you get your component done, your processor or one of the card companies will add an additional security element, or make a small change to the way transaction data should be presented, and you'll have to go back and fix your control. You can expect 1-3 updates per year, on average.
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