There are hundreds of crash repair garages all over the country. Their job is to repair crashed or damaged cars.
Mostly this is paid for by insurance companies. These companies don’t want to pay out more than they have to so they have categories to protect themselves. The decision whether to write the car off or not is purely and only a monetary one. If you think it is based on the damage you are wrong.
The decision to call a car a write-off depends on its value. An older car with a scratch on the bumper may be a write-off and a newer version of the car with extensive damage may not. Insurance companies take into consideration personal injury, car rental costs and recovery costs as well as repair costs. The result is that cars can be uneconomic to repair. The only difference between a crashed car that is repaired by one of the hundreds of crash repair centres and a write-off is money. I examine many hundreds of cars per year. If the repairs are done properly I do not have a problem with it.
However it is best to buy a straight car unless you get a substantial discount for the adverse history.
If you buy a crashed car make sure it’s repaired properly and discounted.