Existing laws apply to repair shops as well - warranty is just as legally binding as anywhere else and they can't sell you dangerous part like say exploding bat

Existing laws apply to repair shops as well - warranty is just as legally binding as anywhere else and they can't sell you dangerous part like say exploding battery. That's the certain minimum. You are claiming that people will always pick the cheapest repair but that's not the case in any other market. Similarly as you are not always picking the cheapest food. Even if health inspectors do their work flawlessly, (wishful thinking,) there are more factors to consider besides price so you check the reviews and there is correlation between quality and price.