i don't see how this would work, where I live MAC has a webstore where you can buy anything direct and get free shipping with no minimum order. worldwide orders are free if over $100.
even if you had a 40% discount, after payment processing/ebay/advertising and shipping fees wouldn't your margin of profit be around the 5% range at best? unless you made your own out of their pigments.
also I used to work for ebay as a chat rep. I saw multiple limited accounts in chat sessions with users crying MAC shut them down for unauthorized retailing on a daily basis. they, like designer bag companies hire law firms that spiders ebay for millions of suspicious keywords then ebay yanks your account without any appeal.