Knock it off.

http://forum.csmania.ru/viewtopic.php?p=608706#p608706

Selling steamgifts invites?

There's many other places like that, and there will be many other people who will try to sell them. You can't stop that, unless you would restrict invitations in one way or another.

The only thing people selling invites like this are going to achieve is the point-price of invites being increased to prevent it...

I definitely would encourage banning those who sell the invites, the ones who bought the invite though shouldn't necessarily have any action taken against them though.