Wow, I'm surprised that when searching on this very topic, there were no replies in a year and a half. I just attempted using the guarantee and am waiting for a response. I did get needed help from a customer service chat in how to fill it out. Without help, one could not possibly fill it their firm correctly. Key points are the reservation number you enter in the provided field and the price you enter is your higher price. The record number field is left blank - it's for people who need an e-receipt. You enter the lower price amount and its associated reservation number in the comment section.