My truck broke down and I had to get a mechanic to diagnose and repair it.
How awful.  Do you know anything about mechanics? I wish I do.
All I know is they quote a price to fix it and it always seem to cost more than the quote
Yes I hate that I don't know if they are overcharging me, I hope I knew at least that.  It seem to be the same for repairs or remodeling my home.
I always follow through when the mechanic suggests preventative maintenance in the hopes it will prevent an expensive repair later. i
Does it?  I always prefer to take time to consider those and don't be rushed in expending more that I should.
I think mechanics are more trustworthy with the maintenance than with a repair
I don;t know and the point is that you can never know if it helped or not unlike the repair.
In the case of parts that wear out over time I have saved money by replacing them before they wear out and damage something else