>Where does this money come from? In theory those posting liquidity will reduce the bid/ask spread, those that are taking liquidity will see a reduction in fri

>Where does this money come from? In theory those posting liquidity will reduce the bid/ask spread, those that are taking liquidity will see a reduction in frictional costs of buying and selling costs. It is the reduction in frictional costs that generates $$$. That and being able to have an edge in whatever orderbook/microstructure you are playing on.