Guess you missed the part where I mention about PPI. Unless of course, you don't consider PPI as part of your due diligence. Kidding.
When it comes to the running of the car - especially the used ones - and inspecting everything under the hood and beneath the car, I would rather take the report of a trusted or reputed mechanic than go by what my eyes convey.
My bigger point was that our site (+ PPI ) can be trusted a bit more than the other sites.