This is Excellion from Runescape. I'm here today to tell you how I made my current 50m. (Edit: It's 80M now!)
About 5 years ago when the free trade and wilderness were vanquished from the game, many people thought merching was impossible.
Many people found out that it wasn't, and it was more like real world stocks.
Also, if you understand real world stocks, this guide will be very simple for you.
This is updated for the new free trade.
Step 1: Finding the Item
Finding your preferred item
0.2m-1m: Lobsters, Coal Ore, Swordfish, Iron Bars
2m-5m:Rune platelegs, Rune Scimitars, Rune Platebody's, Death Runes
10m+: Bandos Boots (My prefered), Dragon Boots, Berserker Helms, Dragon chainbody.
If you do not want to do any of these items, just check the Grand Exchange Guide page on www.Runescape.com and look for commonly purchased items. Make sure your item's price isn't dying.
(Thanks Kelsey >.>)