Folk etymology
Folk etymology wrongly advocates that the word "carcamano" is composed of two separate words. "Calca-" drawn from the Italian verb "calcare", which means "to press down" and "-mano" (IT) meaning "hand". The idea was to refer to the foreigner, probably of Italian origin (whence "mano", vs. Portuguese "mão"), of pressing down on the scales when weighing goods in the dry goods or grocery store. It is a way of calling the vendor a cheat.