Wealth is an abstract representation of money and valuables used strictly within the scenarios of the game. PCs primarily use Wealth to purchase Gear. Wealth only models those things that can be useful within the confines of the gameplay systems; it does not model any extraneous assets, such as housing or land.
A PC can have liquid Wealth represented as a number kept track of with tokens or a notepad. A PC's total Wealth is the sum of any liquid Wealth plus the Wealth value on all owned Gear cards. Liquid wealth is often earned as a reward.
The table below provides the expected Wealth that a PC should have as they begin each level of play. This may be modified somewhat in the case of an easier or harder campaign. It's okay and expected for there to be some deviation due to potential for missing out on rewards, paying to heal injuries, or finding extra rewards. However, if a PC gets a level or more out of the expected range, the DM should take steps to correct this.
The Wealth entry on Gear cards provides the amount of Wealth needed to purchase the Gear as well as the amount gained when selling it. Generally, Gear is sold at its full value; PCs do not permanently lose Wealth as a result of selling unwanted Gear. However, at the DM's discretion some Gear may cost more than the listed value or sell for less. This can be because of in-game economic considerations, rewards or penalties for scenario success or failure, or for game balance reasons (to correct an existing Wealth imbalance, for instance).
PCs can only attempt to haggle on the price with the DM's permission. When allowed, this often results in an interaction scenario. However, this should be rather uncommon as it's time-consuming and potentially game-breaking. It should be assumed that, within the game, PCs are haggling the minute details of the price, but not in an amount sufficient enough to modify the abstract Wealth value listed. Haggling on price should most frequently be used in situations where Gear would otherwise be increased in cost to purchase, such as in the case of a DM permitting the purchase of rare treasure cards.
For more information, see Player's Guide Chapter 7: Gear and Wealth.