I do not have first hand knowledge of such a market, but the idea seems like a natural extension of the markets to sell matured player accounts for online games. If there's a benefit to having a well-seasoned reputation associated with a login, then there's a market for selling that login.

I've heard multiple cases of people selling Slashdot accounts with interesting/low user ID's on eBay, so clearly there's some market for that. It's a stupid product, but clearly the market is there.