There may be many reasons like people prefer to shop on eBay or people just have no brain! LOl sorry I didn't mean to offend anyone. hehe but main reason would probably be those that aren't from USA! Like in New Zealand, our prices are crazy over here, you in American can get a MAC lippie for only $16.00 and in NZ, one MAC lippie cost $45.00! Crazy right? MAC usa site sometimes accepts international credit cards which is amazing! but downside is they can cancel your order if they feel like your international credit card isnt qualify enough! haha I don't know this has happened to me so many times due to them not accepting international credit cards.
So if Nordstorm doesn't sell this one lipstick that I desperately want, I may have to turn to eBay for the more expensive one. But of course, I would avoid buying MAC off ebay.