Although the Black Market Dealer did have a weapon on him, as he was in an unarrestable suit there isn't much that he can do. If you want an actual roleplay reason for this being denied, the police officer can't really be forced to put his life at risk like that.
if you want a reason quoting the rules
These jobs are here only to keep the streets free of crime, this means you cannot be corrupt. There should always be an attempt to arrest a suspect unless; the suspect is resisting arrest, engaging in combat or raiding.
He was unable to arrest the person in question.