Obtain a receipt from the tour company you take on in Italy. In fact, you need a receipt for everything in Italy. Laws in Italy require all businesses to give customers receipts. If your tour company doesn't give you one, it's a surefire sign of a black market operation.
Study the prices of your tour company. If they offer you what seems to be an incredibly cheap deal, avoid them. All tour companies in Italy have set rates and very cheap rates don't happen there.
Check to see if the tour company has insurance. All you have to do is ask them, and if you don't believe it when they say "Si", ask to see proof of the insurance. A tour company in Italy without insurance is definitely black market, with a typical scenario of hiring young tour drivers with no experience. Should there be an accident, any injuries you have wouldn't be covered.
Ask the tour company if they accept a credit card. If they only handle cash, you'll know instantly that they're black market.
Be wary of tour company drivers who drive tourists around in a van without requesting seatbelt use. Don't get on the van if you see this happen since it's illegal for a tour van to do tours throughout all Italian regions without seatbelt use.
