Overcharging, particularly in state restaurants, is widespread in Cuba. Common-sense precautions include insisting that your bill is itemized, asking for the menu with your bill so you can tally the charges yourself, and always asking to see a menu that has prices listed alongside the dishes.
Paladars are less likely to get their maths wrong than state-run places, but are prone to adjusting their prices according to the type of customer (although this isn’t an unheard-of practice in state restaurants either). There’s often not a lot you can do about this, but bear in mind that it’s most likely to occur if you’ve been guided to a restaurant by touts, who collar a commission from the owners; or sometimes if you’re seen pulling up in a state taxi, so try to get dropped off a short distance away.
It’s common for waiters to talk you through the menu, as opposed to showing you a printed menu, and though this might simply mean that the food on offer changes daily, it can also be a sign that you’re being charged more than other diners – at the very least clarify prices when ordering.