Could You Buy Something in Bulk and Resell It?

Could you become a part time instructor at the local scooba diving club? You could probly do the same thing with hand gliding or flying and become a flight instructor. Buy something in bulk and then resell it. Can you eliminate the expense of something completely? So instead of paying for a storage unit which holds your stuff, whyn', you just sell your stuff, have it on cragg's list.