Most of the obvious defects like tile not level can be detected by just dragging your shoe all over the place. The cos are good only if they do IR/thermal imaging to check for leaks.

Test pen only indicate presence of AC 230V.

It won't tell you:
Wires not screwed tightly or at all in socket (only way is to turn off everything and open the socket to see); 230V easily jump across small air gaps or poor contact. Moment I open the socket the wire already dropped out on its own accord
If neutral and live cables are reversed colour code. Swapped or wrong colour codes used can and will happen.
If green supposedly earth is connected properly or even at all.

Always assume the previous joker is an idiota when working w electricity. Test all wires not just the one that looks like the live colour.
Testing more never killed anyone.
Lack of testing, well they not around to complain..

You can use a socket tester to be more precise, or if just want to confirm got power, use a cheap lamp will do.

For checking scratches on window pane, come at night and use a lamp to see, it show up easier than in daytime.

In my past life I used to sell and commission inverters/motors/sensors. So I don't really believe in paying for something I can check myself use my own shoe to test. Shoe with tread patterns will catch on uneven spots easily. Botak shoes just glide over.

Electrical wiring, especially focused on the terminal connections of sockets and switches. should be opened up and inspected [turn off the entire DB box before start work] ⚠️

Check for loose connections (falling out the moment you just opened up) or epic fail jobs (screwed on to insulation rather than the copper). #zerotrustpolicy