I am writing this because I got quite angry seeing quite a few obviously fake designer bags bidding up to hundreds yesterday. I am no expert but I have successfully avoided buying fakes following the steps below. It is less technical than some other guides which you may also find useful:
1. A comprehensive guide to spot fake Louis Vuitton: Click
2. A more general guide I found useful this morning: Click
3. A more technical guide I found useful this morning: (search for "burberryworld.com/index_files/spot.htm" because eBay does not allow links to outside of eBay in guides) It applies to all designer bags.
If this makes things more complicated for you, here's my preliminary guide. It has more to do with common sense, something you may loose when you come across a bargain you feel obliged to grab, or when you are too into auctions and would not give up until you outbid all others.
1. Avoid listings without specific mentioning of the item's authenticity. There are two kinds of counterfeit sellers on eBay, one sells fakes as fakes and one sells fakes as the real thing. It is hard to say which is more ethical, but both make their listings ambiguous about the authenticity of the item by not mentioning it, avoiding responsibility for it (selling for a friend, unwanted gift, ...) or by putting things like "100% ....(new, genuine leather, mint condition, bargain)" which lead you to assume that it's 100% genuine. If you really want an item without specific mentioning of being authentic, take the trouble and contact the seller and if it's a first type seller, they will let you know.
2. Avoid repeated items. If a relatively high percentage of your search results of luxury brands turns out to be the same bag, it cannot be coincidence. Luxury items are supposed to be exclusive, not something some 10 people would unwant and sell at the same time.
3. Minding the description details. A friend bought a Chanel bag here for half of the price at retailers and the seller says it's from House of Fraser....The seller gets the retail price wrong by some hundred quid?....Seller has received negative comments of selling counterfeits? (buyers risk of getting negative feedback for a reason)....blurring picture....a mini lin speedy has a unique serial number...a weird tag attached to the handle....a stick-on with price on the side of a LV wallet gift box....Too many things can go wrong with a poor fake, don't let it slip your eye.
4. Be more alerted even when you think it looks genuine. Fakes are manufactured according to different quality standards as well. The worst ones can be just anything of a manufacturer's choice with a logo stamped and the best ones are exact replicas with authentic dust bags, original boxes, carrier bags, serial numbers and even receipts from known stores and these are the ones that usually rip you off big time. They will be hard to spot from pictures and the best you can do is consult e-catalogues, friends, forums other than eBay's (I am not sure if you are allowed to do that here) and so on before buying. I have avoided buying a Super A-Class replica very recently by consulting other forums. And if it is worth it, have it authenticated at an authorised retailer within the period PayPal provides protection, don't rush to leave a feedback before you do so, which will be misleading to other buyers.
5. Mmmmm...yes less popular designer bags are replicated as well. Don't you think that just because they cost slightly less than the super big brands unauthorized manufacturers would leave them alone. Be careful when you buy Vivienne Westwood, Juicy Couture, Mulberry, DKNY.... even Kiplings (though I doubt for this one it will be too big a difference).
Mmmm, thought about more things before I started writting, will keep updating it with my other thoughts. It's really more of a reminder for buyers to stay calm and think rationally before placing a bid. Hope it helps in some way.