First of all I would Like to point out to you guys how hard it is to come across Balenciaga bags. Some of the larger specialty goos stores such as bergdoff goodman or net-a-porter.com doesn't sell them. So they are very very hard to come across so usually they go for market price or well above market price. If you see a seller listing a balenciaga for less that $500 it's a fake. I'm sorry but that is tha harsh and true reality. If it seems to good to be true it's not I assure you.Check if the seller has more than3 of these bags sold...check the price odds are if the seller has more than three and of the most demanded colors i.e. black white or red they are fakes. I've compiled this guide to make sure you don't get scammed with a fake.

Here are some guidelines for B-Bags:
1. Ask as many questions as you can. Any legitimate seller who
has nothing to hide will answer all your questions thoroughly. Many of the 'fakers' won't even respond to your email!
2. Ask for more pictures - and as detailed as can be. Then look at the pictures carefully. Some of the fakers will buy a real bag, and then use those pictures to sell the 'fakers'. Make sure to inquire "do the pictures represent the actual bag?"
3. While all the Balenciaga bags use the "Lampo" zipper, pictures of the zipper don't necessarily "make the bag"! Take a good look at the leather on the bag. Balenciaga's distressed leather is soft, supple and very light (that's why I love them for traveling!). It should be crinkly all around. I've heard that they take the leather and basically beat the hell out of it - that's how they distress it!
4. The bags are all very squishy ... they shouldn't be able to stand up by themselves unless the insides have been stuffed (mind you - the latest pony and canvas bags are a little stiffer - but not by much). However, not all of the leathers are exactly the same. I find, for some reason, that the darker (Black, Brown, Indigo) leathers have a softer and squishier texture than the ligher colors (Seafoam is softer, the Berry Red is a little waxier, etc.).
5. Pay attention to the Controllato Card. An authentic card is a thicker card stock - not flimsy like paper.
6. All the new bags come with a dust bag, extra tassles, Balenciaga tag (some are silver plates, others are leather - especially older bags). The Metallic bags typically have a plate that is also metallic - for instance, my Pink Metallic has a Pink Metallic plate inside.
7. Shoulder straps are on the City (now called the First) and City Classique (Medium-size) bags. Shoulder straps DO NOT come on the Office (Work) or Weekender (Voyage) bags - EVER!!!!!
8. See if you can get a copy of the receipt to prove where they bought the bag (I'm really horrible with this though - I always seem to lose them in the throes of my excitement!).
9. One of the other trip-ups that the fakers make, is with the color! Sometimes, I have to laugh at the auction text ... such as "Extremely Rare ..." --> TRANSLATION: Never even a color that Balenciaga Made .Check around ... some colors are available for a season only!
10. Check the hardware. Most of the times, it is brass - not silver. However, some of the new bags do have silver hardware (such as the Pony bags and some of the new Metallics). The old Metallics had matching hardware (e.g., my Pink Metallic has Pink Metallic hardware).
11. A serial number should be behind every tag, and the imprint should be a nice deep one. Serial Numbers aren't necessarily a good way to authenticate a bag as they can be easily duplicated. However, the top number represents the LEATHER BATCH that it came from and the bottom number is the STYLE NUMBER. The fakers usually have all the same Batch numbers because - a) they may not know the current number and - b) it's too much of a pain to change them all around!
12. My favorite - the tassles and the loops. The tassles are tied in a particular way on a real Balenciaga bag. Look at a real bag to see what I mean ... the fakers are usually tied very simply (like you would tie your shoe!). Also ... an easy way to spot a faker is that the leather on the ties themselves should, just like the rest of the bag, be light and supple. If the ties practically stand up themselves or seem to be in a straight line, then I would question the bag. Last but not least, the loops should be COMPLETELY SOLDERED!!! For cripes sakes ... this isn't a cheapie bag! If the loops aren't soldered, then I guarantee you that at some point and time, you will look down at your bag and see that the ties aren't there anymore - get it?!?!?

So, there's my 2cents (well - a lot more actually), but hope that helps!!!