am I correct in my assumption that the vendor of the ghost bottles was actually the murderer? or was the cop/shopper arresting the vendor simply for selling the ghost of a murdered person?
I think you can read it either way. Or additionally: if the vendor wasn't the actual murderer, that he colluded in the murder.
I thought it was just the latter. What I don't get is why capturing the souls of the murdered is illegal when everything else seemed fine. But was the end of the story to mean that the cop actually ingests the ghosts he comes across while busting crims like the old guy here, a paranormal twist on the cop who deals with the pressures of the job by engaging in risky behaviour, or did I misunderstand?
As far as why capturing murdered souls is illegal, my take was that it had more to do with the trafficking and profiting off of a violent crime against someone, as opposed to a natural death (Old guy who had a heart attack while having sex).
Inhaling the ghosts (heh...I love that I just wrote that) to me was kind of like a cop in deep cover who must engage in the crimes he's trying to prevent to make the case. In this world, they needed to verify a murder victim's ghost was being sold, and taking a taste is the only way to verify that. So, my read was that it's similar to what you mention, except it's actually a job expectation.