I'm sure since you were in retail that you never asked for ID when accepting a personal check since you, and everyone else by extension, is honest, and above cheating a business or individual. :)
The campground has no way of knowing you're an honest and above board individual except your word for it. Shoot, I could gin up a "doctor's excuse" for why I couldn't show up at some place. It's a shame you lost your deposit, but they were completely open about their policy and you went into it with your eyes open. C'est la vie.