In the constant lore for the most authentic (whatever it might mean) food experience while i am exploring a place, i have developed a checklist that allows me to tell wether a restaurant is a tourist trap or not.
I think that this approach is both useful to the explorer and to the city as an organic being: the first can enjoy an experience, the second will benefit from it as it battles against touristification and homogeinization of things.
First sign of a proper restaurant is an handrwitten menu stuck on the entrance wall, possibly featuring grammar mistakes and cryptic abbreviations. I am not talking about the shabby-chic chalkboards with the wooden-frame-recycled-out-of-pallets-freshly-painted-in-ivory-white, nor anything even remotely fancy or artsy; what you should be looking for are paper towels where a bony, greasy and possibly hairy hand quickly jotted down what's for lunch today and then proceeded to hang them on the front door, adding yet another layer of cheap adhesive tape.
Bonus points for illegible calligraphy (forcing you to interact with the hosts), grease stains and ink from previous menus leaked on the one you are trying to decypher.
As you are looking for a place where to eat, around 1pm try to stalk carpenters as they leave construction sites to have their lunch break.
More often than not you'll end up in a tiny restaurant with lights dimmed by grease and year upon year of casual cleaning, heartwarming food, smiles from fat elder ladies in the kitchen, dubious looks from the other customers, cheap wine and a tiny bill.
Should you find yourself in a place with english menus only, leave the premises as soon as possible.
The presence of translated menus is acceptable only if, in the plastified english menu you are given by the hosts, the amount of typos and the colors used render the translation useless or possibly harmful.
Bonus points everytime the lady behind the counter explains you the menu with gestures describing each passage of the cooking process.
The choice of the precise meaning of such a strategy (cultural pornography, the exploitation of one's image of a foreign civilization or mere search of exotism at the expense of a society's normal mutation) is homework left to the student.