The first sign this place is gonna be authentic is the fact that it's tucked into the back of a grocery store. The next sign is that they serve their tacos correctly, with soft corn tortillas.
Additional notes: You can pick drinks out of the cooler in the grocery store, though they do have Horchata at the restaurant. Their quesadillas are not made with flour tortillas, but more like corn meal dough - fatty and delicious!
Oh, and the staff there has always been ultra-friendly and polite.
My favorite Mexican restaurant in WI.