Bizarrely enough Tesco actually do offer catering services, this was a total shot in the dark because I wasn't aware of it when I wrote the comment before
https://cateringmenupricesguide.com/tesco-catering/
I still wouldn't trust them for something important like a wedding though and I can't imagine many others would unless budget was very strict..
Anyway somewhat besides the point as it was only really a throw away comment and not the main thrust of the argument
Yes they should in theory be held to the same standards, but you'll never good as good a service from a busy overworked big chain business as you will from a small local company who wants you to come back
you're probably right the main point really was find a decent garage (check reviews etc) and additionally, as with any thing you pay someone to do, get more than one quote, I usually try to get three for everything I do. And that's a lot if you include work (sparkies, using suppliers and subcontractors) so I know its a pain, but it's worth the effort