Implicit in answer.

Cleaning of visible surfaces … which includes all contractually defined cleaning services of visible areas, and, as a matter of principle, a check of the areas covered by the complete (or comprehensive) cleaning service.

In other words, they clean the visible surfaces as defined in their service contract, but they also check the areas which are cleaned when doing a complete (or comprehensive) cleaning (which presumably includes areas that are not necessarily visible...)
I'm sure you'll be able to come up with a more elegant turn of phrase.

The following reference may be of help:
Sichtreinigung (cleaning of visible surfaces only)
· Definition: Sichtreinigung ist eine besonders schnelle und oberflächliche Reinigung und gehört zur Unterhaltsreinigung. Es werden nur alle deutlich sichtbaren Verschmutzungen entfernt.
Zur Sichtreinigung gehört zum Beispiel, die Aschenbecher auszuleeren, herumliegende Papierstückchen aufzuheben und Griffspuren zu beseitigen (siehe abwischen).
www.sign-lang.uni-hamburg.de/HLEX/Konzepte/L6/L632.htm

You will also find Vollreinigung in the above ref., but only in the context of dry cleaning, not in the context of janitorial services.

Anyway, HTH

da es sich hier ja um Arbeitstaetigkeit handelt. Der Satz ist wie schon vorher bemerkt grammatikalisch nicht korrekt. Er wuerde mehr Sinn ergeben, wenn das "und" ein "um" waere.

Cleaning of all visible surfaces is a final supplementary cleaning operation. In this connection, all procedures involved in the cleaning of visible surfaces as defined in the supplier's contract will be carried out, including as a fundamental component the inspection of all aspects of the full cleaning process.

very close to PaLa in content. more context would reduce the amount of guesswork.