That's what we have regulations for. If the shops follow the regulations and have the appropriate certifications we know that the work they did is up to spec. A

That's what we have regulations for. If the shops follow the regulations and have the appropriate certifications we know that the work they did is up to spec. Also, obviously in case of some problem the inspectors will check for the root cause and if the repair shop is established as the reason they are liable, not the train company. This is all established law since .. ages. This is just the next episode in an age old battle. Old cars were easy to repair, so people often went to independent repair shops. Companies obviously didn't like this, so they started using proprietary screws. Then laws were made to forbid this. Next round came when cars got computers and companies didn't give the repair shops the required software and/or hardware to work with them. So, laws got made which forced them to. And so on. Each time there's some new technology companies will try to find ways to misuse it to the detriment of customers. And each time law makers will have to get involved and put the screws on them. And then people later go around "why do we have so many laws" .. because companies are shit, if they can get away with it. It's their natural impulse.