That's a common trick used for popular parks. Say you want to spend a week at a very popular campground. You are allowed to stay 3 weeks, you only want one. Book a site 2 weeks prior to plus the week you want (book all three weeks) when the booking window opens (some are 6 months, some 9, whatever). This way you have your campsite 2 weeks earlier than anyone else would. A couple of weeks later, when you're within date, cancel the first 2 weeks. You pay a penalty, but have the site of your choice.
Fair, no. Ethical, no. Happening frequently, YES! Sad but true.