A real Coach bag is expensive which is the reason why there are fake ones because they almost look like the real ones and they are affordable. Here are some few ways I've learned from others on how to know if it is a fake one :

1. C looks like G
2. the sewing is really bad
3. when you hold the bag it's rough
4. the cloth/material is cheap
5. the zippers/buttons,etc don't have a C or coach on it
The best way to have a real one is buy it from Coach website or stores but expect that they are expensive. But I found this Coach Shoulder bag from this website who said that their items are original because they got it from factory direct. coach outletwww.cheapcoachoutlet