Two other things to think about.
If you don't get on with your instructor or the CFI, or perhaps you're unhappy for some other reason, you can't just vote with your feet and move to another school.
Also, I used to be very friendly with the instructors at a flying school and used to often drop by for a cup of tea in their ops area, so I often got to see the operation from the inside. If ever there was a scheduling problem, one of the first things they found out was whether either of them had pre-paid. If so, it was the pre-paid one that got bumped because they already had the money. Anybody who hadn't paid yet got priority because it was guaranteed extra income.