The thoroughness of a CPO inspection/refurbishment can vary from "We did all 200 items the manufacturer specifies" to "We washed it".

https://www.youtube.com/watch?v=f037K2Fr2FU

Have anything I can read instead of sitting through 12 minutes of a talking head?

If it is a true certified, the checklist (standarized by the manufacturer) will have to be signed off by a factory-certified technician, so there is a paper-trail.

and we all know that a car dealer would never do something like sign off the checklist without actually having done the work. /s

Well, as always, a certification is only as good as its certifier.