First, of course, we would want to check the leather. Balenciaga has this distressed look. The leather Should not be too shiny. Please see photo below.
Second, check the hardware, especially on the straps. The authentic bag has this rounded hardware, while the replica has sharp edges and is wider.
Check the Lampo zippers too. The authentic bag has a smoother, not too shiny lampo zipper.
Lastly, When you check the interior, the stitches on the tag that has the heat stamp Balenciaga should always be black, regardless of the bag's color.
It should not be the same as the bag's color except of course if and when the bag is black .. :)
Also, check for the parts that should not be there. Like these hardware on the bag's bottom that are not supposed to be there.
Remember, they make look the same on first glance, but you will not miss a replica by keeping these guidelines in mind. Happy shopping!
For authentic designer hand bags, please visit: https://www.facebook.com/toopretty.tohate.3?fref=ts
Photo ref: First photo from http://members.ebay.com/ws/eBayISAPI.dll?ViewUserPage&userid=luv2shop-hate2spend
All other photos were taken by yours truly .. :)