It depends on the shoe but, fake Air Force 1's and Jordans you start looking at the outside soles of the shoe. They are usually miscolored, sloppy in detail, and light weight. If there is a box, look at the color description. Fakes will have a simple listing of of "red" and "black". Nike official products name colors such as grey "graphite" or black as "obsidian". Most fakes will also have fake leather and stitching. If you can, look up the website of the vendor on bbb.org.