if you buy an hour block but your flightschool still prefers you to fly with a representative, you still paid for the hour, you're not receiving training, it's your hour, you're PIC
You need to be very careful about this. I have known places in the past that do flight training and allow renting but only with an instructor on board for insurance purposes. In this case the instructor was required because the insurance required xxxx h total time, in which case, regardless of who paid for the hour, either you were not PIC or you flew as PIC in contradiction with the insurance requirements. The PIC MUST BE DETERMINED PRIOR TO FLIGHT. This is so important when you have a PPL/CPL/ATPL flying with a FI friend/club member/someone who wants to come for a jolly.