1. A method of auditing a transaction, the method comprising: receiving, at a processor, data characterizing the transaction, the data including a first price for a travel service to be provided by a service provider; determining, by the processor, a second price for the travel service based on a pricing rule of the service provider; determining, by the processor, if the first price matches the second price; in response to the first price matching the second price, allowing, by the processor, the transaction; and in response to the first price not matching the second price, determining, by the processor, an action based on a set of transactions that occurred prior to the transaction.