All in all, investing only promises great returns to those who knows how to play the game right
Investing - Probably the most profitable but also the most difficult to master, requiring insight to values of things. The only rule to this route of kama-making is "Buy low Runescape Gold, Sell high". With great variability of prices in effect, what one deems to be 'expensive' could be seen as 'cheap' by another, and vice versa.
You wouldn't want to be stuck with a piece of equipment that you have no use for but also can't sell it for a profit.
The risk involved is no one knows for sure what is the price cap of any item is but it's inevitable that prices keep going higher and higher because rare items are behaving just like antiques, with the value almost always increasing with the number of times it changes hand.
All in all, investing only promises great returns to those who knows how to play the game right.
Remember the Two Golden Rules:
1) An item is worth as much as someone is willing to pay for it.
2) An item is worth nothing if no one is going to buy it.
Here it is a Dofus guide of leveling 1-200. I think it can be useful to some people here. If you are interested in the article, have fun in game.