I've bought a couples of products from Ebay lately. We don't have Sephora where I live so some brands are not readily available. I find that it helps me sample products (I can buy smaller sizes, usually they're gift-with-purchase items) for a lot less money!
For example, I wanted to sample the Estee Lauder Idealist product. I went to a department store, their smaller sized bottle is something like 60$. For 10$ shipping included, I will receive 2 small bottles of that product, and together they have the same amount as half a regular bottle!