Budget shafted me once for an extra day's hire and a tank of petrol plus £10 filling fee despite me returning the van with a full tank of petrol. I only found out when I got my Access statement. They won that one: "Prove it".
A firm in West London on the A40, who have since gone out of business, let me off broken bumpers. It was a new Renault 25 which got taken away by those nice parking people in Westminster. When I collected the car next morning both bumpers were broken in two places. I took it in to the hire people, the boss glanced at it and said "Fair enough, you were taken by the parking people on a low loader. All our cars end up with broken bumpers because of that". The nice man at the Police pound said "What you gonna do? Take the Met to court? Ha, ha! Now, eff off to work." (One of the reasons why I, a white, middle class, professional person who was brought up nicely refers to the filth as pigs.)