When people ask questions like this they want a sure thing. They don't want to lose cash, but unfortunately in any sort of risky venture there is no sure thing. I do not spend my time merchanting, but I do take up good deals if I happen to see them in banks when I'm in there. If you see someone selling logs or ores for a few hundred less then people normally buy them for, then get them- even if you do not sell them right away. It's not about getting discounts on rune medium helms in the thousands and selling them right away to make millions, it is about carefully buying and selling when you see the oppurtunity.