This is a really good permanent way to earn your money in Runescape.
The main point of this method is to buy low and sell high.
This flipping method will guarantee a 10% or more increase in your initial value per day. (If you start with 1m, you will end up with 1.1m at the end of the day.)
Here's the few tips you need to know.
1.) Need to max buy limit on the Ge. (There's a max on how many you can buy every 4 hr.)
2.) Be sure that the item is stable. (You will not want to buy junks.)
3.) You will need patience for some items to sell.
I recommend starting with cheap items like logs, food, runes etc.
I will use cooked sharks as an example. Go to ge and buy 1 cooked shark for 1000gp above med. (Way above mid) Note down what is the price you got for the shark; for me I got it at 920gp at the time of this guide.
Next, sell that same shark for way below mid at 500gp. Note down the selling price; I got 900gp.
So what we got here, the shark's price range from 900gp to 920gp.
So now you buy 20000 sharks at 900 ea and sell them at 920 ea.
In this example you earn 20,000 X 20 = 40k profit per flip. (One flip is approximately 5mins due to it's high demand.)
So now that you know the basics of flipping, you can use this method to try on other items.
First try out on food, logs, runes, ores etc. Then proceed to low armor like barrows armor. Slowly increase your investment for greater profit!
Maybe you can try to flip rares when you got enough $$
I've flipped santa for 5m profit in 1 min.
Good luck and please be patience with your flips! I always leave big flips on sale overnight.