So, as you guys know, the v.1.2.0.15 patch updated the mercantile mechanics of the game. I did some quick math, and I think I found something that checks out:
Taking a Cave Hopper Steak as the item being sold by a merchant, and a mercantile effective skill of 61 (Six!!):
Starting value when sold by a merchant (at 0 effective mercantile): 1250
Value after mercantile price reduction: 945
Therefore
(945/1250)*100% = 75.6% [The Cave Hopper Steak is sold at 75.6% of it's original price]
100%-75.6% = 24.4% [61 effective mercantile provided a discount of 24.4%]
24.4/61 = 0.4 [Each point in effective mercantile skill gives a 0.4% discount]
Reverse calculation check
1250 - [1250*(0.4%*61)]
=1250-305
=945
Interesting... I wonder how the mercantile of the previous versions of the game worked. That is a question only the developers can answer...