quien no te conozca que te compre 18
It is also used with the third person: Who does not know it to buy it. Saying taken from an Andalusian tale about a donkey, collected by Juan Valera and Fernán Caballero (Cecilia Böhl de Faber). He reproaches someone who despite appearances is a phony like the donkey in the story who was actually a student, according to Uncle Candido.