Here's something that might help put things in perspective.
I grew up in Detroit,im not a big ole tough guy but i have seen some shit in my day,ive also been to jail twice,the first time for Manufactiring & the second time for Felonious assault with intent to do great bodily harm(fancy name for Attempted Murder).
On the second conviction my story was much like yours,i was robbed at gunpoint,mother fucker put a pistol in my eye & made me empty my pockets,i gave it up too but i stayed pissed over that shit.
I ran into the guy who robbed me about a year later,i saw him but he either didnt see me or he didnt recognize me,either way i had time to think,all i could think of was that mother fucker laughing at me when he left,i went to my truck & got a tree limb & proceeded to beat him within an inch of his life,the mfer kept begging me to stop(please sir) & i told him dont hand me that sir shit,shit was funny last time we met wasnt it,i beat on him till he was a bloody mess then took everything he had on him including his shoes which i threw in the street.
Of course i got picked up,on the stand his mother told how his life was forever changed & what a good son he was,his doctor gave a report about how his bruised heart will most likely never heal right & that i ruptured his kidney,then all about how much pain i caused him,the guy who robbed me even swore that he never saw me in his life & never robbed me.
I ended up doing over 2 years on that one but it was the best lesson of my life,fuck that chump shit,assholes like the guy you know will always call the cops on you after you get revenge,then they'll laugh while your doing time,or they come back stronger next time so it never ends till somebody gets seriously fucked up.
Let that shit pass & learn a lesson,the lesson being dont buy anything from anybody you dont know personally or send anybody else to do a run for you,getting back door'ed is all part of the shit that comes with it & you knew you were taking a chance from the start.
Walk away from that stupid shit & leave his ass to the real gangsters who will rape his mother while his father watches after he rips the wrong person off,and he will.