Obviously, you don't want to waste hundreds or thousands on fake shoes. The first thing to remember is only shop at legitimate websites. If you're concerned, just search for the name of the store plus the word "scam" or "knock-off." If there are a lot of bad reviews, you know to stay clear.
Also, if the site promises extreme deals where you get $1,000 shoes for just $100, you might want to avoid them. While you might get a once in a lifetime deal like that, odds are, it's a scam.