To try and convince someone to make whatever they are selling a lower price. They'll suggest a price, you'll suggest a lower one, and each of you keep on suggesting prices until you are willing to pay.
Slang for Weed.. back before weed prices were pretty much standard $25/50 - $30-60. You would haggle over what you were willing to pay for a bag. Hence the term. It is used when referring to weed over the phone.
(ring)(ring)...Hello, Yoh, what's up? Yougot any haggle man?