Let’s clear this up quick and in a hurry, Vince did NOT mean to shoot Marvin in the face, but he was being extremely negligent since he had his finger on the trigger, a round chambered, and the safety off. Reading a variety of stances on whether or not this was an accident one can only come to one conclusion: Vince is a truly horrible gangster. At the very least he’s a terrible trigger man since not only does he shoot someone in the face, but in a couple of other instances he’s seen to make things worse or not do his job in a way that would make sense. Marvin’s unfortunate shooting is something that could have been avoided even if made obvious sense for another plot point that would keep the story moving. But for Vince, this was just another mistake in a line of them that he would make in the movie. When it comes to being trustworthy it sounds as though Marsellus trusts him implicitly, otherwise he wouldn’t have allowed him to take Mia out for a good time, especially after hearing just how protective Marsellus is of his wife. But knowing that, the actions that Vince takes throughout the movie are kind of hard to figure out since he doesn’t exactly play it smart at all times.
Stepping away from Marvin’s uncertain fate for a moment, let’s go to the apartment scene that saw Jules and Vince lamenting the fact that they didn’t have shotguns for the job they’d been sent on, the same one that would see Marvin in the back of their car by the end of it. Knowing full well that there might have been several people in the apartment they didn’t bother looking past the front room and the kitchen, despite seeing only three people. They’d already assumed there were more, so why didn’t Vince go searching the apartment while Jules covered the main room? Sure, he needed to find the case, but securing the location should have been the first priority to avoid any surprises that could have been the end of them. Another thing about Vince comes before the two enter the apartment and then after the job is said and done, when Vince goes to take out Mia. First off, he gets high before taking her out, perhaps to calm his nerves and mellow him out. But it’s still a bad idea since at that point his judgment is impaired, he’s a little loopy, and despite appearing okay for the most part it’s obvious he wasn’t thinking too clearly. Then there was that awkward silence that a lot of people might have felt was something more when it happened between Mia and Vince. Hey, things happen.
But Mia’s overdose, despite not being all on Vince it was a good part of his fault since if you’re going to pick up your boss’s wife it’s best to leave such things where they can’t be easily found. That’s kind of a sticky situation however since who knew that Mia would end up wearing Vince’s jacket? He’d already convinced himself that he was going to take her out, have a good time, and then leave for the night. But his moral conundrum after the awkward silence made Vince fret so much that Mia had plenty of time to snort a line and mess herself up in a big way, enough that Vince needed to act in an even riskier fashion when he made his way back to his dealer in the middle of the night, knowing that the dealer was being watched by the cops, in an attempt to save Mia’s life. He couldn’t go to the hospital to be fair since they would have to file a report, and such a report would have eventually made its way back to Marsellus, which means that Vince knew he would be a dead man.
Skipping over a few things we then get to Vince’s eventual end when Butch shows up at his old apartment, where Vince and Marsellus have been waiting for him. What kind of hitman leaves his weapon just lying on the counter, or holes up in the bathroom without a good line on the apartment just outside the door? Had the door been opened, it’s likely that Vince could have pulled a gun, if he still had one on him, and ended Butch then and there. But somehow, whether he was high or just being negligent again, he was caught unaware and was ended in a burst of gunfire that took him out of the equation. Like it or not, the character is great and a lot of fun to watch, but he’s not that great of a hitman really, since he made a large number of mistakes that should have gotten him killed a few times over. Poor Marvin was, unfortunately, a byproduct of Vince’s negligence.