We have been boarded only twice in Roaring Girl (so far). Once by the UK Customs, in 2005, in the Thames Estuary, primarily as a training exercise for some newbie who'd never been on a blue-water yacht. They were very polite, but it was still four men with guns. The second time was in France, in the Ile Porquerolles, when they checked our registration papers.
Otherwise, we've shown papers at various ports and that's it.
This week the Cabinieri have been very busy in Elba. T'other day they boarded another boat in Portoferraio. That vessel doesn't carry a captain's licence of any sort: they're not required in their home country. The police told them that they should have such papers here in Italy and threatened them with a �'�3000 fine! Fortunately they decided the paperwork wasn't worth the hassle and left them alone, leaving the crew pondering their approach to such things.
We checked our papers and dug out our International Certificates of Competence, just in case.
We saw the same vessel visiting a yacht anchored off Biodola when we walked there. And yesterday they visited an Italian yacht right next to us in Portoferraio. He didn't have an anchor ball up, and was fined and made to hoist something. (He chose a black bin bag stuffed with something and tied up like a toffee.) The police ignored the several other non-Italian yachts flagrantly disregarding the rules around about and returned to harbour.
We'd got our paperwork ready and were happy to be visited, but obviously we weren't interesting.
So, if you're sailing to Italy be prepared with the documents and have an anchor ball to deploy.