What are the tricks to avoid buying fake bags on ebay ?

Other PFers have already provided some great advice, here's my $0.02. There are a lot of honest sellers selling authentic items that are described accurately and honestly. And, there are a lot of dishonest sellers who use all kinds of tactics to make a quick buck. In order to tell the difference, educate yourself on the particular bag you want to buy - if possible, go see it in a store and really familiarize yourself with the details, and post a link to the website here in the appopriate authentication thread so other experts can help assess authenticity - AND educate yourself about eBay, including researching the seller's feedback/past items sold and familiarizing yourself with some of the cheap tricks dishonest sellers use. Finally, use common sense: for example, if you're after a super hot/just released bag that's selling at full price in stores, don't expect to get an authentic one on ebay at a discount.
 
The more I think about this, the more I like the "mentor" idea. I agree with balihai about education, but just a brief and cursory browsing around here will give you an idea about just what a massive amount of education would be required.

The people on here who are experts, these Leading Authorities on everything this or that or those particular design houses have ever produced, as well as the increasingly complex labyrinth of eBayology, did not acquire that Leading Authority status overnight.

These are people who have put in some serious time, and for some of them, the subject is a major focus of their lives, they have dedicated more of their personal intellectual resources to it than to anything else, so to clarify if there is a need for it, I just don't think that it is possible to just make a list of tips for someone who simply wants to obtain a designer bag at a bargain price!
 
ALWAYS ALWAYS Read feedback left and feedback received by your potential ebay seller. Check the items sold/purchased if still available. Make sure the seller has been on ebay for a while. Make sure the seller doesn't sell the same bag over and over by checking completed listings.
Contact previous buyers and ask!

When I purchase a new handbag, I always keep the receipt. Therefore it is sent and photographed when I list a handbag on Ebay.
Do an internet search on the seller. Yes, this would be how prospective buyers would find out about paparazzi-girl aka monaco-babe, etc etc.

And finally, if the handbag is still available, it's best to purchase at the boutique or saks.com , neiman-marcus.com , bergdorfs.com or eluxury.

Hope this helps!!
 
definitely post the auction on an authenticate thread. People here know their stuff for the most part. Also, I intensely read buyers' feedback. One thing that I do is ask the seller to send me more pictures of the item. Too many sellers steal pictures from websites and other sellers. If they say they can't do it, or they don't answer, I don't bid.