New guy next door seem shady. Should I investigate?

A new guy just moved in our apartment complex about two or three weeks ago. Everything was fine at first. Didn’t make that much noise, keeps the hallway clear, etc. Then, a week ago things started to change. Some girls would come up to his place until like wee hours of the night. At first I was like wow this guy must be a charmer but I found it really weird for groups of ladies to come up frequently. Like in the morning about five girls would go in then another batch on the afternoon...you get the picture. I was able to gather a bit of information from the lobby. Apparently the guy’s running a foreign marriage agency of some sort. My gut says otherwise though. I have a feeling he’s running like a cyber den or something. Should I trust my gut and investigate further? It’s really bothering me to live beside him.