Venice lives on tourism and the hospitality industry, so it is very rare for a restaurant or hotel to be unscrupulous, because the penalties are severe. I mentioned upthread that a restaurant overcharged four Japanese exchange students for a meal. They informed city authorities that they were overcharged, and showed the receipts. The Mayor did a prompt investigation, fined the restaurant 14,000 euros and closed it down upon finding the students complaint to be true. That's why I've never seen or heard of an unscrupulous restaurant in Venice, except this case that received a lot of media coverage because a group of tourists were ripped off.
The Mayors response was first only in Italian, but the newspaper announced that he wanted to reach as many tourists as possible, so he had it translated to english. You can read what happens to an unscrupulous restaurant in english here.
Hospitality is sacred in Venice: we will punish these dishonest people - Cronaca - La Nuova di Venezia