Getting valid numbers

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When looking at the mls it’s hard to believe the numbers listed. How do I dive deeper into a listing to find if the numbers are accurate. For instance looking at a 4 plex. It says after expenses, NOI, 30k annually. Is this realistic? Rent amounts seem realistic but not sure if they aren’t including capex or setting aside repair reserves monthly to make deal appear better. Can a 4plex really generate that much annual income?