Use the basic principle of if it's too good to be true it probably is a fake. There are numerous knock-off Fendi purses and wallets out there. So many in fact that one could be easily confused. These purses and wallets unfortunately are being sold as genuine. Look carefully at all pictures prior to bidding. One MAJOR difference is the snaps. Genuine Fendi's will have the word FENDI on the snap. Many fakes, either have not marking or have some unknown marking. I purchased a wallet that I thought was genuine until it arrived, and I was able to clearly see that the snaps did not say Fendi.
DO NOT rely solely on the box and wrapping. Knock-off brands also use Fendi-like boxes and tissue. Also, if the seller has external websites, you may want to explore these as well. I bid on a Fendi purse, and then researched the sellers other websites. She claimed on Ebay to sell only genuine. However, her other website was for knock-offs. When I questioned her she said she sold both. However, she was unable to tell me how she determined which ones were real and which were imitations.
I like to inspect seams. If you pay close attention to seams, you can tell a great deal about the quality of the materials and workmanship. Seams on genuine Fendis are always straight and even, without irregular or uneven stitching. Linings on fakes are often sewn in an inferior manner or made of inferior materials.
One last thought, read back in the seller's feedback. You may have to look way back to see if there is any question of fakes. If so, it is highly suggestive that the product is a knock-off. Before you buy something this costly from an unknown seller, and if you truly want GENUINE, do your research and a little detective work. Always remember - if the deal is too good to be true, your Fendi is probably not a genuine.