Billionaire and Aon Plc Founder Patrick Ryan sold his stake in Mu Sigma Inc. after learning the founder said the data-analytics startup’s prospects were dimming. Eleven months later, Mu Sigma raised millions in fresh capital at a much higher valuation. Ryan wasn’t happy and sued, arguing Mu Sigma’s founder bought back the stake for an artificially low price and set himself up for a bigger payday. Expect a lot more lawsuits like this. Listed companies must give all investors the same important information at the same time. Private companies have more leeway. But an explosion of “unicorn” startups valued over $1 billion and more opportunities for smaller investors to buy and sell stakes has made the market for pre-IPO companies more like the public equity market. As a result, investors are pushing for startups to behave like their publicly listed counterparts. Even the Securities and Exchange Commission is starting to poke around. “Most of these unicorns do not practice best practices. I think they violate some of the core securities laws,” said Ken Sawyer, co-founder of investment firm Saints Capital, which oversees more than $1 billion.