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If you issued a tax receipt, there very well might be.

But would a thief sue them for this? Would be fun to see someone sue them for no disclosing declining payment from a stolen credit card!

Probably not, but as mooism2 mentions, what happens when it's a legitimate customer who gets wrongly banned?

That will be a little bit of inconvenience for them. But since they don't get shipment or get charged, they will most probably contact customer care and get themselves unblocked.

If they are not charged and then system tells that order is sent, that is not much harm. I know, not the best condition for a customer but acceptable to stop cc fraud!

you could say that the transaction went through but don't send an actual order confirmation by email to fraudsters. As far as I know carders will quickly try out a bunch of credit cards to see whether the charges went through but they won't stick around and wait for a confirmation email if the checkout screen says that the card has been successfully charged.