I'm a gringo who's been working in Mexico for the past 4 years and I had absolutely NO problem getting my FM-3. It was a headache mostly because my Spanish was terrible at the time and everything confused the hell out of me, and most people (keyword MOST) did not seem to have the patience or desire to help me.As for the Tax Administration Service (SAT), I made an appointment and even though I unfortunately didn't have all my documents that day (mostly my fault), I simply made another appointment, went back and took care of everything right then and there. I don't mean this in a condescending way at all, but if your plan is to wait tables, why even bother trying to get your FM-3 and pay (30%?) in income taxes? Mexico is very lenient on illegal immigration so I wouldn't stress over it at all. If your plan is to work for a multinational where they have you on payroll, almost all of them have at least 1 person in HR who specialize in immigration issues (I work for a professional services firm so I kind of speak from experience).