Hello,
I would check the inside of the purse for the label (Louis Vuitton) and also look at the material/fabric inside the purse which will sometimes have the signature name (at least Prada does). If you are still not sure take the purse to a Sak's Fifth Avenue or similiar store that sells the name brand purse so they can check it out and tell you if it's fake or not.
Good Luck!
~T~