In Venice you find high quality food, however with tourists staying few days there is really no incentive to offer good quality for money.
Quadri St Mark Square
Restaurant Oro at Belmond Hotel Cipriani
Da Fiore in San Polo
Venissa Fondamenta di Santa Caterina
Steer away form restaurants with multi language menus outside and waiter chatting to you convincing to go inside. Most common complains are that in the set menu no drink are included and then when ordered are very expensive. Another error that tourist can do is ordering fresh fish price is for 100 grams, not for unit.
Unless you can afford be careful when sitting around St Mark Square especially enjoying orchestral music as it may prove very expensive like 20 or more Euro for a coffee.
We Recommend in the city centre Rosso Pomodoro for excellent Neapolitan Style Pizzas.
A good place for excellent and Cheap Tramezzini is Rialto Bar 3 minutes walk from Rialto Bridge. where with 1.80 Euro can fill yourself.
As general rule if you see a place you like check their trip advisor review before entering. Like in most touristy places there are some tourist traps better avoid.
GELATO You will be tempted by walking in Venice of this delicacy. Look carefully the best is artisan made with real fruit and best ingredients. Avoid buying industrial made one served as artisan