4 tips for buying Diane von Furstenberg dresses for cheap on eBay

I've averaged $81 (including shipping fees) for buying 43 dresses on eBay.  This is only dresses I still have in my possesion, not including dresses I've sold back.  How do I get dresses that usually retail for  around $400 (with tax) for 20% of the price?

1. Know the goods.
2. Know fake from real
3. Know your size
4. Know your price limit

Know the goods--have a good, working knowledge of what a Julian, Jeanne, Justin, Jessica, Jillia and Jude are.  Browse Saks, Bloomingdales, DvF.  Know what dress styles are.  If someone puts up an unnamed style, it might be a genuine dress.  I've scooped up some dresses for very little due to a bad picture or unlabeled style.   Also, as you don't get to try on, know what the dress looks and feels like. 

Know fake from real.  Here's an article on some quick tips.  In general, look for a style tag!  Look for pictures!  If the only picture is a stock picture, ask for more.  If it's labeled as New with tags, ask to see a photo of the STORE tag.  

Know your size.  Are you a small 2?  An 8 that can squeeze into a 6 or upsize to a 10?  If you've never bought a DvF, try on a few at a store to get a feel for what they are sized.  Be aware that wraps can be dramatically different from fitted dresses.

Know your price range.  I'm willing to pay up to $150 for a highly desirable dress but would like to pay under $100.  Don't get caught up in a bidding war.  Conversely, when a dress I want (China Vine Olivier) appeared, I bought it for very close to my limit.