Okay. I'm not sure if this is a bug, but it is highly exploitable if not.
Items such as powders can be sold for the same price, regardless of how many times they've been used. This means you can take, for instance, sneezing powder, use it 4 times and then sell it on, without losing any money. It would make more sense if the selling price was reduced with each use.
The same goes for picks. If I remember correctly I sold my pick which had 0 uses left for the full selling price.