You cannot win any money at all since it is a play-money site. They do offer in-app purchases, so some people spend money to buy chips. I did know a guy who was a pretty good poker player and he won billions of chips and then sold them to other players at a price cheaper than Zynga sold them.
Definitely rigged, for example the spin wheel on spin and win 85% of the time spins the lowest amount of money not random at all. Also, the red numbers never hit on the wheel. You will never win in Zynga. It is beyond rigged.