I myself have been a victim of fake fragrances on E bay. I had not been using E bay very long and my experience and knowledge of the site was very poor, I obtained Christian Dior Midnight poision August 2010, this was a present for my daughter advertised as sealed and unused, both myself and my daughter have used this fragrance for quite a few years. on opening the fragrance and spraying we both noticed right away this was not the correct fragrance. Having said all that I have been succesful in purchasing genuine fragrances on E bay. These are my rules when bidding.
1, If the photo has no background, Its fake... always check the photo is natural in surrounding. eg: bedroom, bathroom ,kitchen, etc..
2, If it has no packaging thats good, more chance of the real thing.
3, If its Half full, three quarter full... its a good sign again its genuine.
4 If in doubt always check out sellers other items, if its good stuff, varied and used another good sign
5, If still in doubt ask for the serial number on base of bottle..
This is the 5 If's I use when bidding for Fragrances on E bay.
Good Luck! And remember there are genuine people out there