One of Marc Jacobs' most successful items in his eponymous line is the Stam bag, named after model Jessica Stam. Since the bag was first launched in 2006, new variations of the design are created each year, all keeping the same shape and quality of materials. Most versions retail between £812 and £1,007 each, so to be conned into buying a replica could really hurt your pocketbook.
Feel the material. Stam bags are almost all made with a soft leather body, usually quilted. If the material feels like plastic, you are probably dealing with a fake. The bag itself should be a hexagon shape.
Inspect the hardware. Stam bags almost always have gold hardware, including a clasp opening, which can be easy enough to replicate. However, an easy sign to know if you have a counterfeit is if the hardware is not all uniform in colour. Compare the strap, any studding, zippers, handle rings and feet to make sure they all match. If they do, look closely at the zipper heads; they should read either Lampo or Riri.
Check the interior to make sure that it has inside zip pockets, as all Stam bags do. The lining should be sewn in, never glued, and you should see a country of origin plate stamped with "Made in Italy."
Make sure the chain strap is detachable. This is an easy step for counterfeiters to overlook, even though it is present on almost all Stam bags.
Look at the quality of work. One of the reasons this bag is so expensive is because of the amount of work and inspection that goes into it. All seams should be even and aligned, threads should not be frayed and any details, such as studding or quilting, should be uniform.