Just off the train in Florence, from the relative quiet of the Cinque Terre in the north where we had either walked or taken the train, we waited patiently for a bus to take us to the neighborhood we’d call home for a few days.

Finally, we hopped aboard. I had my €3 ready and had practiced, “Due biglietti, per favore,” in my head so I could politely request two tickets.

The driver shook his head, and apparently sensing my actual level of linguistic knowledge, said — in English — “Buy at the tobaccoist.”

We slunk off the bus, tired from the day’s travel already, and went in search of a tobaccoist. The first one we found — back in the train station — displayed a large sign announcing that there were no bus tickets for sale at that establishment. A kind gentleman nearby directed us to a machine near the tram stop outside another entrance.

Now, why didn’t I think of that? Go to the tram stop to buy tickets for the bus that I didn’t know I couldn’t buy tickets on.

Tickets in hand, we trekked back to the bus stop and soon boarded the bus to home. We saw other riders feeding their passes into a machine so we followed suit. All was good.

This rule of buying tickets before boarding the bus (usually at the tobaccoist, but at other nearby businesses if there isn’t a smoke-seller) apparently applies throughout Italy.

The next day, the validating machine didn’t work and we rode without thinking anything of it. We’d bought a ticket. It wasn’t until another day that we learned how lucky were not to have been caught with an invalidated ticket.

We’d seen the transit police move through the buses from time to time. They’d randomly board at one stop, have a little chit-chat with some riders and get off a stop or two later.

But then a French couple near us on this afternoon had tickets that did not have the requisite time stamp. Did they understand the rule? How long had they been in Italy? How many rides had they taken on those same tickets?

In the end, they paid a €40 fine each — on the spot, with a credit card. The receipts they got could be used for one more ride (and, they were reminded again, not to forget to validate them).

Had they not paid on the spot, they would have had to dish out the money at a post office (no doubt requiring another bus trip) within 14 days. And lest you think that leaving Italian soil would absolve them of the debt…the cops had taken down their passport information.

Buying tickets and validating them is truly on the honor system in Italy, but be honorable. If you get caught, it’ll cost you.