I love guerrero's!  I worked in Mesa 15 years ago and we did burrito runs here all the time. I'm a huera, but my Hispanic pals all rated this place authentic.  It's a husband and wife team that runs it.  The best thing are the beans - incidentally, that's how I rate the authenticity of Mexican fare- They are the kind of beans I ate in Nogales during college (at a place I could only locate while intoxicated).  Thinner, lighter colored, and delicious compared to any I've EVER had this side of the border.  I live in PV now- super far - but after this I think I'm gonna have to take a road trip tomorrow to Mesa! Yum!