Resale of makeup... How?

There is a girl at school that is selling makeup to help her mom. her mom lost her job so they are selling makeup (like cover girl and revlon) to help pay the bills. They sell it for discounted amount than store bought I think revlon eyeliner is $3.00.... ANYWAYS what im wondering is how are they able to sell brand name makeup for cheap and get a profit. I would ask her but i feel it would be rude