Mukaka is an ethnic slur used to describe immigrants of darker color, particularly shop owners and salespersons. It can be used to refer to people from Africa, the Middle East or the Indian Sub-Continent. It emerged from the large scale internet phishing operations where victims were promised various forms of get rich quick schemes from a desperate "Chief Mukaka" of an Indian or African tribe. It has a similar connotation to word shyster, but with obviously racial connotations.
Stop trying to rip me off Mukaka.