For economy in the game - there is currently none. There is no trade and there is no real “sink”. The current merchants are useless. Waste of space. Since the player currency is time merchant items should reflect that. Silver in Sepermeru should for example not be very valuable there. In the city in the djungle silver should be more valuable, but gold not so etc. Wood is everywhere so that you cannot sell, same for stone and iron. That you can only buy, not sell.
I also like the idea of having furnature merchants. Perhaps carpet merchants that sell carpets only found with that merchant. If merchants sell more of social items and resources then I think it could work. Merchants shouldnt sell legendary items or high level items. Resouces (save time grinding) or social items (for example carpets).
I like that idea, to combine Missions and Reputation-mechanics with merchants use.
If player reputation is neutral for that faction the price to buy is for example 10 gold, selling same item to that merchant gets 1 gold. If reputation is positive the price to buy is 5 gold, selling is 2 gold (Merchants should always pay less when player sell them items. ). Negative reputation then no purchase can be made.
One fun thing with having reputation combined with merchant is that you can add merchants that does not care about reputation but is super expensive instead. Also, you can add a priest of Set that sells antidote 10 bottles - if you sacrifice to Set (50 gold?) but purchasing it comes with negative rep for the other factions. Same exist for the other factions. This is a social merchant, ie. doesnt really affect game play but for those that want to RPG and not have all dietys at once this would be fun imo.