First of all please remember one important rule related to eating out in Greece - select restaurants with a character, those where locals dine. The presence of local people in a tavern constitutes the best recommendation for a place! Don't pay much attention ot places lacking local character.
Taverna Petra is locatedin the main square by the bus station so you won't miss it. It serves good local food at decent prices. You can take a nice table in the center of the square's roundabout. There is a small and miserable fountain there.
Favorite Dish: God, I don't know what my favourite dish was :) I'm a semivegetarian so I had to compose my meals from appetizers. It was worth trying :)
Definetely worth a warm recommendation is this nice fish tavern run by the Papadakis family. You'll find in on western end of seaside promenade of Kastelli.
Enjoy its friendly atmosphere, wide variety of local specials and perfect sea view. The host tends to speak at least a few words in all languages of the world. Unless he's very busy, he'll do his best to entertain you with a chat.
Credit cards are accepted. By the way, Lonely Planet also recommends this restaurant.
Favorite Dish: Let me draw your attention to huge portions of ever tasty tzatziki (EUR 2.50) and state of the art boureki (EUR 4.50). Take a bottle of Kissamos retsina, the best choice in local wines. I also recommend cheese saganaki (EUR 2.50).
Upon the receipt of a bill you'll receive a small portion of grandma's pie and a shot of tasty rain on the house.