It seems like at least half of the gym chain business model is to get people to pay without actually using the gym, so that seems entirely consistent.
This wreaks fear into most merchants, not only because fraud policies at banks greatly favor the buyer, but also because too many reversals within a certain period can cause a payment processor to charge higher rates on all transactions indefinitely, sometimes even if the merchant always cooperates.
Edit: Also usually works with most check cards, but I've come close to losing with them a couple times, whereas real credit cards are practically bulletproof in my experience unless you're just attempting some kind of egregious fraud.