Love seeing little data like this. This explains why my main character had better bartering than a companion with higher charisma. The first time I encountered the Grove merchant, I had pressed barter without pressing the scales when learning how to sell. I was too lazy to reload the save - I usually over-loot anyway so it wasn't a big loss.

Also seems like a good opportunity to have Wyll chime in when you revist the Grove Merchant with him in your party - have a line of dialogue that hints at this system.