I've never had a problem with a gift card. I've used them at four different Marriott properties. Never had to educate anyone. In fact, the employees have educated me: "Sir, we can put all of your charges on the card, no additional credit card is required."

Having said that, I wouldn't mind having an official sheet of instructions/information that I could hand a desk clerk if needed. I'll slip into my briefcase, right next to my United Airlines Contract of Carriage