Sorry about that dude, my stepdad got that once, some big black dude with a sawed-off shotgun. He was gonna get back at 'em too but he decided not, an he's a tough guy.
Option 1: Intelect
While the gun is in your face, be calm, cool, and collected. Tell them they can have whatever, if they can kill you, and that you'll certainly not let them do it without a fight. Then eat away at their emotions, goin' over all tha bad stuff they've done, and how they'll go to hell. Tell him he ain't go tha ballz to pull the trigger, and make sure he doesn't, for obvious reasons, wittle away at him, eat at his mind. Tell him the gun isn't even loaded and whatnot. Ask him what good it'd do to kill him for some cash, with the cost of his freedom, his life, his soul. If you pull it off well, he should give int or just leave. Or turn himself in. Of course, you'd have to be part insane and have an influencin' personality. And you'd probably be sayin' this as you run or go in circles around one another. Not for the average joe with an average intelligence.
Option 2: Force/Deception
Tell him you'll give him tha cash if he drops tha gun (at quite a distance away), then reach into yer pocket to get the goods. Then, with items in hand, get as close as you can, then strike in a fight finisher area. Punch him in tha adam's apple, push his nose back into his head, take his legs out from under him, hit him in the gonads, etc. Then pick up his gun and point it at him, then lead him out of wherever you're at (assumin' a back ally) and take him to the nearest cop. Probably your best option.
Just my best ideas, maybe you should just not go into the bad parts of town anymore.
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