It has also been documented here previously that the €50 offers for servicing can't be doing a fully comprehensive service, it just isn't economically viable.
There was nothing said about a non comprehensive service. They were advertising a cheap service so as to get work. If they couldn't do the job for €50 they shouldn't have attempted it. And there is a difference between a not comprehensive service and leaving a mess after the service and refusing to tell the customer what was done.