The knock-off can be spotted by examining the logo. The logos on copies are never exactly the same as the original. Inferior hardware and material are also signs of copies.
Knock-offs are sold at house parties at a fraction of the cost, and real one are sold in department stores, or specility shops. Give a good look at the stitching.
People who make knock-off hand bags are often very good at what they do. You can look for small clues as to whether a bag is a fake or not. The threading will not be done as perfectly and you will be able to see small flaws in a fake bag. The logo is in several places ona real one.
Authentic bags will sit upright and appear sturdy. Check the stitching and the label inside the bag. Your best bet is to go to the brand's website, print out a photo of the bag & the inner label. Then use the photos to compare when purchasing a bag.
it depends on what bag it is, a lot of times, the stitching will be different from the authentic version. Sometimes there is also a bar code or something similar that proves that the bag is real