It's a hybrid-exchange. An exchange meaning you wager against other players, not the site. You do not post bids and offers based on odds, the site calculates all odds at true vig-free (overround correction) and keeps them updated. That is why you see NY Knicks +187/Indiana Pacers -187, for example. True-vig free, good luck finding better on either site!

You can think of it as a vig-free bet matching service rather than an exchange. Someone can post for the Knicks, someone else comes along and wants the Pacers, then they are matched and a bet is created. You can see the open orders (people listed directly under the side they want, with amount) - but you cannot see what has already been matched. So the liquidity is greater than what is visible.

Feel free to pm or email with any other questions!