How can bit walls be fake?
They must have the funds to place them and if they are got hit the transaction is done.
Well I must be psychic because *POOF* the $4 wall has vanished.
Yes, the person putting up the wall (mtgox) has to hold enough to cover it, but since it's fake, and there's no intent to follow through, the wall disappears (gets cancelled) before any trades get close to filling the order.
http://i.imgur.com/dHqUa.png