I agree that is a bit fast to flag an account as being a fake, I usually give people 7-10 days to leave feedback before I'll start thinking about flagging their account.
However, I do also report these fake accounts as I see them, and encourage anyone who sells coke points or even looks through auctions for coke points to look for and report fake accounts. It is really very common. You just have to look for:
1. Bidders who just activated their account within the last week. 2. Bidders who WAAAY overbid on coke points, paying sometimes 10X what they would normally go for. 3. Bidders who don't leave feedback for the seller. They will usually have a few auctions won under their account in which the seller has left feedback for them but there is no feedback from them on any of the auctions they won.
If they don't contact you then you get the credits And keep the code... use it for another auction. If you're worried that they won't ever leave feedback for you then you can have yours removed from the auction within a month of the auction ending so they don't get it either. This is a first for me, I must be missing something :)
I don't even know what these codes "normally" go for but if I need 20, 40 or whatever to get something I want from MCR then it's worth it to me to spend more credits, so I can get my Prize. I'm in :)