Know the market. Be wary of units that advertise significantly lower price points for comparable apartments in the area.
Beware of the words basement or attic. Advertisements that use these words are often for apartments that typically lack adequate exits.
Avoid apartments that have rooms without windows or very small windows. These are often found in illegal cellar or basement apartments. Landlords will sometimes describe the ones with very small windows as “sunny” to entice renters.
Beware of the word flex. Flex implies that the apartment can be converted into a multi-bedroom unit using pressurized walls. The installation and/or construction of a wall without the proper permits from the Department are illegal.
Utilities included is a red flag. A landlord may not want utilities under another name connected to the property because those residents would violate the legal occupancy of the building.
Avoid apartments with odd layouts. They are often described as unique or interesting and are oddly situated (i.e. a shower installed in the kitchen).
Be cautious when a landlord refuses to disclose the exact address. Landlords advertising illegal apartments may ask to meet a potential renter before exposing the address to possible regulation or penalty.
Beware of apartments where you can't have mail delivered. Landlords advertising illegal apartments will often request that tenants obtain a separate P.O. Box.
Beware of no-lease apartments. Be suspicious of a landlord who declines to draw up a lease, requests a month-to-month agreement or requires cash payments.
Check for adequate means of egress (way out) and look out for locked doors in the unit. A tenant should be able to access all available exits either directly from the unit or a public hallway.