Fake goods are different from real ones. Learn the differences and you'll be able to tell whether the vendor is offering you a real designer item or a copy. Pay your money for what is worth it.
1. The finest details
Usually counterfeiters use photos to make replicas of the famous brands. It is very probable that the interior of the item will be very different from the original since counterfeiters make the things look real only from outside. Always check whether the inside of the item matches the designer item.