How Can I be sure it's a chunk of Meteorite?

Just started reading about these "pieces of Mars, etc" and how would I know if what I'm sold is authentic?
I'll be attending NEAF in April and usually someone is selling hunks of Meteors and I've never bought any as I wouldn't know if it's "real" or not. What would you recommend to read on the subject....for a newbie like me?
I've been looking over the samples shown by some of the collectors in this forum and have seen some pieces, at trade shows, which looked like them. I don't know of any meteor collector group, on Long Island to refer to. Much appreciated.

George