It's no secret that I'm a fan of vintage stuff. I buy sometimes things in a shop in my neighborhood called SamSam. Now, I know two great sites that sell real designer items. http://www.fashion-vintage.com/ and http://www.designer-vintage.com/.
Example; Chanel, Louis Vuitton, Alexander Wang, Gucci, Prada etc. But they also have jewelry think of; Otazu, Rolex, Swarovski, Juicy Couture etc.
Often you just can see if the stuff is real or fake. Most of the time its real, you can check that because they almost take a picture of everything. Sometimes even the price tag.
I think its the best place to buy authentic designer clothes, shoes, bags and more!