There’s no stat block for merchants in any of the D&D books I have, so I was forced to write my own.
The special aspect about a merchant is their job; they’re good at buying and selling common and exotic items. A good merchant sets their prices smart enough to make a good profit and still attract those looking for a bargain. That requires a keen eye for pricing an item. So, I made up the Appraisal mechanic, which simply outlines what type of check should be made to work out the value of an item.
Charisma is used when the price is found from socialising with other merchants or even trying to figure out how much a customer would be willing to spend by feeling the general atmosphere around the market. On the other hand Intelligence might be used based on knowledge of the markets far and near – the economy. Charisma is the people-based knowledge gathering, and Intelligence lends itself more to understand the cause and effect of various outside forces.