BEIJING — China is poised to overtake the U.S. as the biggest movie market in the world, but how many people are really in the audience?

After “Ip Man 3” — a Chinese martial-arts movie in which Mike Tyson plays a crooked property developer — pulled in 470 million yuan, or $72 million, over its opening weekend, Chinese regulators said this week they are investigating whether the distributor tried to boost the movie’s box office by buying tickets for “ghost screenings.”