Italy has a law that means all visitors from countries outside the EU have to reported to the state police, it’s simple to do, the form is below. For a list of the relevant email addresses, just go to https://questure.poliziadistato.it/ and search for your area, normally you need to notify the Police Headquarters, so the closest big city in your province is who you notify. You can search on a search engine, typing Questura and then your province name.
The law is very clear, you have to declare anyone that does not live with you within 48 hours if they are not from Italy or the EU. No exceptions. If they stay in a hotel or B&B they do the declaration so you don’t have to.
If an Italian Citizen stays with you, you also have to declare the presence using the same form, but only after 30 days.
The fine if you don’t declare is from €160 to €1000 euros, so really not worth avoiding.
Remember to include a copy of the persons passport or other ID.