Never work for unethical people. If they lack ethics in their dealings with customers, they will inevitably lack ethics in their dealings with employees.
Zynga's product does not provide a worthwhile service, nor does it improve people's lives. It creates no value. Rather, it (cleverly and cynically) capitalizes on weaknesses of the human psyche to relieve people of their money, one dollar at a time. This is an inherently unethical position for a company to be in. As such, regardless of the compensation offered, any prospective employee of the company should ask themselves whether the ethical foundation such a company displays in relation to its customers will extend to employees.
A CEO who is comfortable fleecing customers will feel similarly comfortable fleecing employees. I learned this lesson the hard way in the trades, working for people who would jack up prices and sell material and services that the customer did not need. They would shirk responsibility for deficiencies, and usually try to do jobs for cash so as to avoid paying taxes. Invariably, this lack of professional ethics extended to myself and my coworkers. Cheques would be short, overtime would not be paid, and promises would not be kept.
The best indicator that an employer will rip you off is their willingness to rip off customers. When you see it, start lining up interviews immediately.