An important book to have at your disposal when working with a factoring is The Law of Contracts and the Uniform Commercial Code. This book covers all of the important features of common law contracts as well as Article II of the UCC. Chapter summaries, review questions, exercises, running glossary, and more help students fully grasp this complex area of the law.
If you have a concern or issue with your factor, you'll either have to seek (expensive) legal advice, or possibly educate yourself with this very invaluable tool.