der Halsabschneider — The throat-cutter. A person who takes advantage of others without scruples, a usurer.
jemanden übers Ohr hauen — To hit someone over the ear. To take advantage of someone, to cheat. The phrase comes from fencing, where it meant a blow to the head above the ears.
der Knebelvertrag — The gag contract. A contract that restricts one partner and is very hard for that partner to end.