In Dofus, that you must to know, people sell leathers and wools very cheap, the reason is that they want to buy some weapon skill, better gear, house or other useless things. Make sure you do not rip off people with silly prices, because they will find out very soon that they can sell it for others, for much more, thus you are strengthening your competition.
We always paid decent money for the resources we bought, and this resulted in people farming for them with the only purpose of selling them to me, and this alone gave us the significant advantage of being well-supplied, therefore we could level faster then anyone else, made friends and constant suppliers, future customers. Spend more time around sellrooms and buy cheap resources that are required in crafts, and nobody needs them.
Also, try to get as many cheap in Dofus, otherwise scrolling material that is required in 2-slots, such as mushrooms, thorns, larva skins, arachnee legs. This only applies if the given resource is totally underpriced, which is rare thanks to scrolling freaks. Keep on farming Gobballs all the time and save every leather, wool and Warchief tongue you drop. Sell everything else unless you want to make a Jeweller too.