if you already have a fair amount of money you can go to a store and buy items off the shopkeeper, if he has alot of one thing he will sell them for alot less than their intended price, if you buy all of them, he will not have any left and so will buy them back off you for nearly double the price you bought them, you get the biggest profits by doing this with diamonds but you can do it with anything a shop keeper has alot of
its kinda a cheat but its helped me afew times
Hope it works for you too