aerofoil1, I have been in many situations like that. It happens at all airfields. On top of that you can find the plane you booked weeks ago was out of service and they havent found you an alternative. It's worse still when you have taken family and friends with you.
It's one of the reasons I bought into a share. Obviously the financial implications of that can be high, but there gets a point where flexibility, availibility and the chance to share some flying with other pilots wil open up your boundaries considerably and you might feel less deflated. I am in an equity share, but maybe you could look at a non-equity share ?
I would echo what some of the others have said. Get there at least an hour early; avoid the 0900 slot; book 3 hours instead of 2 so you have some leeway to deal with any other issues or fly a bit longer if you want to; see if you can get the previous pilot to leave it on the pumps or fill it up and not abandon it with little fuel or oil; and ask the previous pilot about any known defects that might not be in the book.