All reports about error in sales such as above are handled by http://www.urban-rivals.com/en/staff/contactus.php
Contacting Forum Operators, Mods and admins won't really help with the problem, we will just redirect you to CSS.
@T0P GUN: reading your problem, I'd say the player who bought your Marco Cr
back in 2009 really didn't do anything wrong. He obviously bought your Marco fair and square in the market. He is not, in any way, responsible for your mistake. Unfortunately, we all do mistakes like this and sell cards only to realize they'll become CR after awhile, we can't expect the technical staff to return all cards sold prior to them becoming CR. That's not how it goes.
On the other hand, if it was an error such as selling your card for 10k instead of 100k the staff will do their best to help with this as it's obvious the extra "0" was just overloooked. Although in saying this, people who does this sort of thing often may find themselves in a bit of a hassle when it comes to trying to get the CSS to act on the problem, as it is each person's responsibility to double check their sales before proceeding afterall.