This e-book provides templates for 21 most effective credit and collection letters that will help you communicate better with your customer. 1. In the sample letter, fill in your personal information.Square offers two free generic credit card authorization forms for download. You do not have to process payments with Square to use these templates. Goodwill letter template. Use this fill-in-the-blank Notice of Credit Limit letter to notify clients when they've exceeded their credit limit. A credit card authorization letter gives someone permission to use your card. Learn how to write one, and when it's appropriate to use it. Get your free copy here! You will see credit letter samples that we offer and all are downloadable.