Brass/bronze 10 and 20 cash coins generally aren't faked, unless they're a rare or sought-after type. This, unfortunately, is one of those types, listed in Krause as KM/Y# A176.1 and worth thousands in "this condition". That, plus the toning pattern that looks suspiciously like the "spray-on toning" I have seen on some fake silver coins, make me assume that this coin is fake, too.
