They're all blaggers and bluffers in my experience and none of them can be trusted to just do what actually needs doing but there's nothing we can do about it unless we take our vehicles to independent specialists first for an inspection/appraisal before we let spanner monkeys loose with their tools. I remember a sting operation on Kwikfit and Halfords a few years back when they sent in several cars for basic services after an independent specialist had already inspected them and passed them as having no issues but every garage charged for work that didn't need doing and replaced parts that didn't need replacing. Garages make most of their profit from the labour charge so the game is to keep your vehicle for as long as possible and keep the mechanics busy doing jobs/repairs.