During the reign of the Sartar Dynasty, the princes minted silver coins, called Sovereigns or Guilders, for use in trade. These were modeled on the silver coins used within the Lunar Empire (called “Lunars” or “L”), having the same weight and silver content, and, as a result, the same value. These coins had very wide circulation, and were used in lands as far away as Teshnos and Ralios. A copper coin, called a Clack (“C”) and modeled on the Holy Country currency, is used for smaller transactions.
During the Lunar Occupation, Lunar silver coins flooded Dragon Pass and the Lunar became the standard silver currency. The circulation of Lunar is even more wide than the old Sartarite guilders, and the silver Lunar can be found in markets as far away as Fronela, Jrustela, and Kralorela – even if none of the merchants have ever even seen a person from the Lunar Heartlands. With the liberation of Sartar in 1625, the silver Lunar remained the main coin in circulation, although beginning in 1627 the new dynasty began minting increasingly large numbers of silver coins.
Gold is primarily used for large accounts, such as trade or tribute. The Wheel (“W”), an ancient coin minted by the Wagon Cult, is widely used in accounts, even if it is rarely seen in daily life. The Sartar Dynasty never minted their own gold coin.
Nonetheless, most daily transactions were in barter. Among the rural tribes, cows, and not Wheels, were the instrument of accounts. Livestock or grain were more likely to be exchanged than silver. These exchanges were largely between members of the same tribe; when strangers or foreigners got involved, coins were preferred even by the most traditionalist Orlanthi.
Note that almost nobody outside of the troll realms accepts bolgs. Which is downright mean of them.
So you need coins to buy that fancy sword or that decorated armor or the bolt of silk, but keep that grain, cattle, and chickens to trade for local wool or to get someone to help you work in the orchards.
Sartar is not nearly as traditional as many people have made it out to be. From the very beginning, Greg emphasised that Sartar transformed the peoples around the Quivin Mountains from quarrelling bandit tribes to a kingdom based on trade and commerce with a substantial urban population.
Remember this is not Ireland, a removed island distant from the main trade routes even during the periods of the port of Dublin. Barter, gifting, and coins existed in Central Asia and the Caucasus from the Achaemenids to the British and Russian Empires. Unfortunately, historians tend to isolate their studies.