Never buy a black suit as your first suit.
Don't listen to this advice. A black suit is fine. Nothing beats a good looking jet black suit.
Wow, that is horrible, horrible advice that I have never heard in my life. Black suits are for night time formal activities or funerals. Law firms are conservative places not a place to make yourself a fashion icon. Navy Blue and Charcoal Gray suits are the most acceptable. Also, never ever wear a black suit on an interview. One reason is like it or not law firms have to purport an image and they will judge you on how you look. Black suits show that you don't what is acceptable in a conservative adult atmosphere. If you want a black suit that is fine but it definitely should not be the first suit of somebody who is going to be wearing this for interview in a professional atmosphere for years to come.
Furthermore, people can tell an expensive suit for a cheap one. It's not very hard. Just take a look at the fabric and one can tell. The way the suit hangs, the way that it is cut. Young people might not be able to tell because they don't have much experience with suits. Lawyers who wear them everyday can easily tell the difference.