Using custom price books for domestic and international customers is the best way to improve usability for account executives who find the standard price book difficult to use because of different currencies and country-specific product variations. A price book is a list of products and their prices that account executives can use when creating opportunities. A custom price book is a price book that can be created and customized by users based on their needs and preferences. By using custom price books for domestic and international customers, account executives can easily select the appropriate price book for each opportunity based on the customer's location, currency, and product requirements.