If they bring a 3.5kg platter of fish along with your spaghetti, question it. If you’ve asked to share something and it looks huge – check it’s only one portion.
Question things the minute they arrive, not once you’ve eaten them. It might not be them trying to screw you over; it might be a simple language barrier.
Compare the Menus
Check the English version of the menu, which is always posted outside, and see if there are glaring differences.
No restaurant will be stupid enough to price the menus differently, but I’ve been to a couple of places where the English menu states “SERVICE NOT INCLUDED” and the Italian includes it in the coperto.