It is extremely common for customers and prospects to have specific questions about billing. Your customer service people should inform you very well on what the common questions are.This is a great place to address billing practices, guarantees, refunds, and if you offer something like pro-rating upgrades.
You can often address many of these concerns with a blanket statement about ‘always favoring’ or ‘always being fair’ to the customer. The most important thing to do with this section is allay common fears. You don’t need a comprehensive product FAQ.
Hubspot has a quality example of this practice.