While you're right to be wary of scams in your search, rather than being offsides, duplicate listings are standard practice in the NYC real estate market.
"Duplicate listings are not a sign of a scam," explains Joe Charat, founder of search site Naked Apartments, but rather, a function of how many landlords market their buildings by using multiple brokers to reach as wide an audience as possible. "There are a number of options available to the landlord, from working with an exclusive broker, to working with a limited set of brokers or an entire open community of brokers. In the event of the latter, there is a high likelihood that multiple agents are going to post the same availabilities, which is why you might see duplicates on the same site."
Adds Citi Habitats agent Santiago Steele: "Some landlords are very big and have a lot of buildings, and feel that working with just one broker or company might limit them."
However, some shady agents do use these open listings as an opportunity for a bait-and-switch, posting photos of a landlord's listing that they don't really have access to, in hopes that they can then lure interested renters to other properties they have on the market. (This is one of many classic New York real estate scams, and while it's relatively harmless in the grand scheme, adds an extra layer of irritation and hassle to the already-laborious rental search.)
While a listing without an address used to be a telltale sign that something odd is afoot, search sites like StreetEasy now require a listing to have an address, which in general is a boon for renters but can also make it more difficult to immediately tell if something is a fake. Still, says Charat, "renters should always trust their instincts if a listing appears too good to be true, or if they notice that difference addresses contain the same listing photos."
You can also do a little extra digging. "You can always just ask the broker about the building, and if they’re exclusive they’ll know everything," says Steele. If they're not—or if they don't even have access to the listing in question at all—that will become apparently pretty quickly in the course of your conversation, and you can move on to the next possibility.