@Ethereal I do not look on this part of code but I would guess that only direct damage give exp, commendations are separate mechanic that have different way to track kills, and this is why behind difference.
On other hand, I push new script hooks for items buy and sell prices, now you can arbitrary change price of any item (global date can affect price too!)
If someone will be determined it could add daily fluctuation of prices that will change at "random" each day (but two cravats, you need roll your own "random" logic as game random is not available in this hook and yours sells do not affect price as its not exposed to script yet).