Many years ago we serviced an old V8 that required a plug change, mechanic found the awkward plug was marked and asked what to do, so he was told to mark the new plug and leave the old set at the
service desk, sure enough two days after collection the customer returned complaining loudly, he was presented the old set of plugs and told that since he didn’t trust us to
service his car correctly he should go to someone he did trust and was told to leave.
No
garage I seen takes the same time and care with oil changes as we do at home, they don’t have the time, but yes there are some who are less than honest, whilst there are others who do try to be the best at what they do, no point complaining here if you don’t confront the
garage, they might not be aware of what the mechanic is doing, I have seen mechanics dismissed for poor practices, it takes a long time for business to build a good reputation and only one poor job to damage that, not happy? First point of call is the person you paid to do the job and ask for an explanation or a rectification.