You must click on the icon Petra is showing you during dialogue with vendors to buy or sell. Anything you loot like food, books, formula scrolls, roses, gloves, jewelery, scarves, alcohol, food, etc. all can be sold to the related vendor. Think about a vendor who would be selling these things and this is the person who would buy it from you. Things that the vendor will not be interested in will be grayed out in your inventory box. Books and formula scrolls are sold and purchased for example by the Antiquarian in town who is also usually located near other vendors selling/buying food, jewelery, herbs, etc. As far as reforging your steel sword with ores, you dont even need a steel sword to do that just the 3 pcs of ore. Sell the steel sword to the vendor at the Armory prior to asking for it to be reforged and youll make some oren there as well. (It defrays the cost of reforging the sword). Otherwise your original sword will be replaced with the new reforged sword and youll lose the opportunity to sell it. The original sword is actually not reforged but replaced when ores are offered which is why the original can be sold.