-The interior number tag is also a great way to determine if the bag you are looking at is authentic. Authentic Prada handbags will have a small white tag in the interior with a random number on them. If the seller of the item you are interested in does not include a picture of this it does not mean the bag is fake. Most established designer handbag sellers on Ebay will include a picture of this tag in their listing. This tag will be in every interior pocket of every handbag.