prior to the sale, the notary is supposed to carry out some preliminary investigations to make sure powers of attorney are valid, the real estate belongs to the said owner and has not been sold to someone else, there are no debts or encumbrances, a.s.o., in other words that everything is ok from the legal point of view so that the sale-purchase may be done. For instance, to check the existence of the real estate in the Land Book or Register, he has to pay a certain charge to that institution, which he later recovers from the client. This is preliminary work and apart from this, the notary drafts the deed and notarizes it by signing and affixing his seal.

http://pluris-cedam.utetgiuridica.it/pdf/dizionario_multilin...

Those expenses related to the investigations that need to be carried out prior to any deed-of sale, etc.

Term used in the UK

The references are self-explanatory:

brief explanation: http://www.globalpropertyguide.com/Europe/italy/Buying-Guide
citation:
The notary performs due diligence
Closing usually takes six to eight weeks. The notaio or notary public has the responsibility of performing due diligence - although he is chosen by the seller, he acts for both parties.

A little more exhaustive: https://www.justlanded.com/english/Italy/Italy-Guide/Propert...

http://www.italianpropertygallery.com/the_costs/
- Highlights the fact that the actual due diligence is undertaken by the "geomtra" (under notarial oversight - see above). The "charges" are therefore not part of the Notary's fees proper, but paid by the latter to the Geometra - the term Geometra is left untranslated, some law firms render it as "conveyancer".

Very exhaustive comparative cost breakdown: pdf file
http://www.cms-cmck.com/Hubbard.FileSystem/files/Publication...
citation: Chapter title:
Due Diligence Costs for the Purchase of Real Estate.

Hope the above was helpful.