Merching is different to flipping in 1 huge way. Flipping is forcing G.E prices to be lowered. Merching is making them higher.
Merching is fairly simple. Find items that will be required soon, for instance event times. If there's a boss event, people will be needing to get some Overloads. Start by flipping the G.E by buying bulk extremes and bulk herbs at say 5-10% lower then sell them on at either G.E price or +5-10%. This is predictive merching though and not always 100% chance in making profits. However, Checking the official runescape website for updates or events that have been announced will give you a general idea of what items will be required. Start to buy them at lower prices than standard G.E price or find a shop that sells them cheaper than G.E prices. Then sell them at a higher price. This will start to gradually change the G.E prices. It is slow for G.E prices to change but they will change trust me. For example, Bonds have gone up atleast 5m now. (quick heads up don't be buying these in bulk just yet i'm sure they will be dropping to between 9-10m soon then going back to 12-14m)
Flipping, is more complex. People usually find items that will be required for skilling. I take a totally different approach to flipping than most people would dream about doing. Making me atleast 60-80m profit per hour. Obviously i had to start out small, Few combat gears (guthan's, bandos, armadyl) that are cheap and easily buy. I started buying them 5% cheaper and selling 5% more expencive. a Scaper in quick need will always press +5% atleast 1-3 times. Tell me you haven't done this??
i started on guthan sets. buy the set for around 5.1m and sell spears for 4.5-5m (they sell eventually keep hanging in) then move to tetsu and malevolent. Before you know it you'll be looking at quick buy and quick sell differences for drygore weaponry. The range is usually between 800k-1.9m which is a decent amount of profit for 5-10 mins of afking. This will come naturally soon and you will start making between 100-300m per day
If this guide is hard for you to follow don't worry, like i said i will be updating it. which includes short clips, Screenies and Q&A's