Can man mode flipping has always been part of the game. What happens is wealthy investor in osrs community buy large chunks of a item over a long period of time. They either are watching something like ge-tracker or some other web service to track their items. Knowing there items and getting sometime helpful updates also is something they use. After a period of time they list there items on the GE, this is a whales game. You need to be either very wealthy in-game or use those that you can relly on to make this possibly. It is part of a private community. Leaks can mess this up. Also if joining a clan that does this expect to be the one not making anything. Look online at GE flipping..... But learning the items, uses and the longevity of the item is the best way you can support yourself on your own if trying to get into flipping.
Best of luck,