You might even want to consider two different forms of credit card payment. Eg: Paypal and 2checkout.com or Paypal and your regular merchant. We've had dozens of instances, where the payment didn't go through one credit card, but worked flawlessly on the second system. And here's another tip.
Right next to the payment button, we put in the words:
If you have any problem, or your credit card doesn't go through, please email us and we'll call you. This has resulted in quite a few people emailing us.
If you want to see the page I'm talking about:
Sean - Moderator
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