When Keyan Sanai moved to Manhattan and started working as a real estate broker in 2014, he was eating 12 to 15 cans of tuna a week to keep costs low. “I said to my friend, ‘My mouth tastes like a fistful of old pennies all the time,’” he says. After a doctor’s visit, he found out he had mercury poisoning. His first few years as a broker were rough. Working at a “boiler room” brokerage, he got acquainted with what he calls the “dark underbelly” of the industry. “The script is basically to lie to people: ‘Put up [an ad] that says ‘no fee’, and once you get ’em…