Many have chaotic schedules - I travel 50% of the time - and my days can be hectic. I’ve had to cancel last minute but I always mention that in case they can book something that’s more certain. Many are turned off by this even when I offer to pay if I cancel last minute but communication is key. If you don’t share details on why you may not be readily available within 48 hours after initial contact, there is no reason for them to not think of you as a troll chatting them up and then flaking on the follow through.