Similarly, I tend to get people thinking I'm a native Spanish speaker when I stick to stock phrases, or sometimes I even get strangers who just start speaking to me in Spanish because they assume by the way I look that I know it.
Guess this question sort of has 2 parts.
1) How easy is it to develop enough of a linguistic façade to fool native speakers of a language you meet on a passing basis?
2) Do you employ any methods for telling people who are native speakers from those who just learned the language really well?
Any language is fair game, just curious is all.