Whether it's on the basis of race, gender, age, sexuality or disability, discrimination can be tough to detect, so pay attention. Another common practice is an announcement that the unit has just been rented. Because you have the right to inspect your credit report, it's difficult to refuse you on that basis, so other scams may be tried. You might be told that you need the first and last month's rent, a two-month security deposit, a key deposit, or the like. You may suspect that others aren't paying this much up front.
Most agents have long lists of available units.
If you are denied access to the lists, be suspicious. Watch what notes or symbols an agent places on your papers. It is not uncommon to find a code indicating race or some form of discrimination that affects your rights to obtain rental housing. All these practices are illegal because a landlord must rent to anyone who can satisfy standard credit requirements, who is not an obvious threat to the safety and well-being of the property or other tenants, and will not overcrowd the unit. About the only exception is restricting children in buildings that are exclusively for people more than 55 years old and that are specifically operated for seniors.