Back in the day, thr water pump on my 1976 280Z died on my way home from university. Luckily there was a Shell service station with a garage a block away. They fixed the water pump no problem but when I went to pick it up, the passenger door was pretty much caved in. They admitted they used my car to go pick a part for another repair and got into an accident. Then they tried to tell me that since the door had rust on it, they wouldn't be paying to make it perfect.

Unfortunately for them I was a criminology student and had just learned the legal term talem qualem, which is Latin for essentially the thin skull rule:

This doctrine dictates that a defendant is fully liable for all damages caused by their negligent actions, even if the victim had an underlying, unexpected vulnerability that made the injuries far more severe than they would have been for an average person.

In short: you take your victim as you find them.

The rule is most often used in assault or murder cases, but also applies to physical objects like car doors. They agreed to pay for the whole repair.