If you experience odd or unexplained amounts of merchant gold, even after the merchant has restocked, then you probably have another mod loaded after Trade & Barter which has altered the VenderGold leveled lists. To resolve the issue either: 1) Change the load order, and make sure that Trade & Barter loads after the other mod, or 2) Click the "Disable Merchant Gold Options" option from the menu. This will reset the Merchant Gold options and allow the changes from the other mod to prevail without further interference from Trade & Barter.
Economists since the times of Adam Smith (1723-1790), looking at non-specific pre-modern societies as examples, have used the inefficiency of barter to explain the emergence of money, of "the" economy, and hence of the discipline of economics itself. However, ethnographic studies have shown that no present or past society has used barter without any other medium of exchange or measurement, nor have anthropologists found evidence that money emerged from barter, instead finding that gift-giving (credit extended on a personal basis with an inter-personal balance maintained over the long term) was the most usual means of exchange of goods and services.