If you've already lived in New York you know what an ordeal it can be to find the right place. If you haven't and are planning to move here, grow a thick skin and practice your anger-management skills. You'll also need to be prepared to spend way more than will actually seem fair and, in some cases, pay fees that don't exist elsewhere but are standard in NYC.
These include the hugely unpopular 'broker fee' - yes, you may well have to pay just to find an apartment. Most buildings are run by management companies as landlords don't want to deal with the hassles of renting or managing them. These management companies list apartments and brokers compete for business (and, in turn, tenants compete for apartments). Typically, a broker's fee will be either one month's rent or 10-15% of the yearly rent. You should be extremely wary of being asked to pay anything higher than this.
In general landlords require you to make at least 40 times the monthly rent per year, or they'll need a guarantor (who needs to make 80 times the rent). Most charge an application fee and will also charge you for a credit check. If your credit doesn't meet their requirements you'll need a guarantor with (again) 80 times the rent and a perfect credit score. The guarantor promises to pay the rent if, for whatever reason, you can't and they may have to actually sign the lease instead of you. Even then some landlords will require more than one month's security deposit - in some cases up to six months. City law is rather murky as to whether this is actually legal or not; it usually depends on whether the building is classified as rent stabilized.
The good news
Thankfully most room rentals and sublets, like those found on SpareRoom, are a lot more relaxed. Most only require a security deposit equal to one month's rent. Sometimes they'll also require the first and last month's rent up front. Most will want to see some proof of employment and some may run a credit check, but that's usually everything.
A note of caution
If you're going to rent a room as a sublet you should ask to see a lease or a deed of ownership. City law prohibits sublessors from charging more than a proportionate share of the rent. Most leases also require the primary lessee (the person whose name is actually on the lease) to inform the landlord about a subtenant (although not everyone does). However you find your room it's important you make sure the person in question actually holds the lease or owns the apartment before you put any money in their hands.
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