Quality test gear, annually calibrated as standard and kept in a water tight soft cell hard case to protect from impact which could impair calibration.
Visual inspection is just a important as the high spec test gear, one cheeky customer making a very dangerous sinario reversing the polarity to get free electric, but in reality meaning when the trips trip the electric will not trip off threatening anybody in the house but most importantly his family and children.
Emergency call out no down stairs sockets, chasing a fault around a ring main eventually finding it and replacing a couple of sections also at the same time found the kitchen sockets were spurred off the ring main so we were able to incorporate the kitchen back into the ring main properly.
Just because the installation works does not mean it is safe, unfortunately words i here alot "but it works"
Build up of heat not only de rates the amount of load a cable can take but also brakes down the insulation or worst case starts fires.