Gold Coins are used as a currency for services in the assassin world.
The currency used in the underworld is mostly gold coins, crafted by a coin maker and approved for distribution by The Continental’s manager, Winston. While their use is universal in this criminal society, there is not a consistent exchange rate. A single coin can be exchanged for any single good or service, be it a knife, an AR-15, a single night at The Continental, clean-up and disposal of one dead body, or a single bar tab. This may be to establish an even playing field among all assassins in which the value of a coin is determined by the skill of the owner instead of pure volume of wealth.
Despite the reliance on the gold coins, assassination contracts are assigned with a value designated in US dollars, possibly emphasizing that value is based on the individual. This would suggest that while any good or service can be exchanged for a fixed value of one coin, the value of individuals is a variable amount.