Can someone explain me how these Multipools work?

They mine other coins and then they buy BlackCoins with the other mined coins right?

How do they buy BlackCoins? Do they put Buy Orders or they go directly to the sell orders?

Whats the buy volume of all pools like this, lets say peer week?

I'm thinking.. If they go always to the sell orders and the buy volume is high, then we will have a BlackCoin infinite increase in value... ?

Any place where I can verify the volume of these pools, and how many pools exist?