Not paying the tourist tax in Italy can lead to fines and penalties, and the establishment where you are staying may pass these fines onto you. While legal trouble is unlikely for a small infraction, deliberate avoidance or a larger pattern of evasion could have more serious consequences. Most lodging establishments diligently collect this tax during check-in or check-out, so it's typically hard to avoid paying, and it's in the traveler's best interest to comply to prevent any potential complications, such as damage to reputation or difficulty in leaving the country, though these are rare.