[Retric]

There are several stages of CC validation. EX: http://www.experian.com/decision-analytics/credit-card-verif...

  M = Full match
  P = Partial match
  C = Match, but account is closed
  L = Match, but card is lost or stolen
  E = Invalid card number
  X = No record or security alert
  N = No match

IMO, you can display an error page for some types of issues without helping scammers. However, for physical goods it's a good idea to wait 24+ hours to display C or L codes to users. That way it's not useful for CC scammers, and you have minimal impact on users. Partial matches or other stages that fail your security checks are up to you.

[giancarlostoro]

Additionally if a customer is a repeated customer you may want to "whitelist" them, assuming they ever need to update their info (card expiration). Just a small tweak so they get feedback right away if they keep coming back.