I've, personally bought makeup off of ebay, but only after I read most of the comments on the seller's feedback by buyers who had bought makup from them and oly after I had made damn sure that the makeup was untouched...and I had a gr8 experience. Make sure there are clar pictures of the makeup you are buying and if the pix aren't clear enough ask the seller to email you clearer pictures. Even if the seller has listed the item as NIB (new in box) use the "ask seller a question" option to confirm--the seller doesn't get annoyed, usually and you now have two written confirmations that the item is as described along with gr8 photos, so if some one hoodwinks you, you can fight back, but that's never really hapened in my experience.
Good Luck.
-Eliza