Assets and monetary gains are covered via a simple Wealth stat, not acute calculations of coin; the fact of the matter is, there are many things which quantify richness in Athas, and coin is often the least of these things (water, land, herds, etc). Essentially, Wealth is scored just like a skill and rolled just like a skill. The distinction is that it has no upper cap beyond what the game master assigns it. Characters begin with Wealth 1 in Red Age games.
Wealth is, as has been said, a representation of the character’s possessions as well as the money a character has. This means a character may choose to detail his or her holdings, describing what makes them so wealthy. Purchasing things with Wealth does not deplete the Wealth score, but rather builds a Debt score alongside it. Debt may equal or exceed Wealth; neither cancels the other out. Debt represents favors, loans, and many other things, including the deterioration of existing possessions – for example, a broken weapon may incur 1 Debt until it is fixed.
Simply put, Debt is a penalty on the bartering and trading impact Wealth would otherwise give. If the leader of a powerful merchant house has 53 Wealth, his bargaining position is rather strong – but as soon as his errant brother accidentally lands him into 50 points of Debt gambling with a Lord Templar, his seeming Wealth to those in the know drops to 3, and his bargaining position seems no better than your common free citizen.
Wealth may be spent to cancel out Debt in downtime, but not during play. The only way to assuage Debt during play is to pay it back in favors or assets directly – doing this during play is considered to be a role-playing solution, not a statistic solution, and the character keeps his Wealth score as-is.