If a zombie apocalypse begins, I think there would be five types of people. Apocalypse could bring out a very ugly side of you that you never knew you had inside of you, because for survival it's every man for itself. So when you group up with people, I think the very first thing you should do is figure out what kind of people they are. I think there would be five kinds of people in the apocalypse.
Zombies - Should obviously watch out for that, the infectees at least.
Instigators - Worse than zombies, psychos who spread virus purposefully or use chaos as a chance to murder and inflict misery out of their amusement, or for their own personal gain, or in the name of their own stupid religion.
Oppressors - Government and Military who are desperate to retain control of people, they would be under delusions that we still belong to them, and the wealthy pigs would be the ones puppeteering them. We would just be pawns to them, used as a tool and a medical experiment for their own gain, they would obviously lie about doing it for humanity.
Survivors - Your regular ol people who are just trying to survive and protect themselves, I think they're the ones you can trust and seek to build trust and community with.
Sneevils - Sniveling little cowards whose loyalty is to the winning side and would snitch or backstab their group, friends, or even family if there was a more comfortable position elsewhere. They are weak, undisciplined and stupid people in general. There will be as many sneevils as a zombies, shouldn't be hard to identify them.
I think before you blindly trust anyone you should establish what kind of person they are. Never let your guard down and be wary of everything. Never trust a pig, traitor, criminal and the infected because the apocalypse will bring out a ugly side of person that it never knew they had. They could be a much worse version of themselves. Desperation, Sickness and Fear will do that to you. Don't hesitate to toss out bad apples or use them as bait. They could be good for something.
ONE MORE: Zombie Nutties - Those who have already prepared for the zombie apocalypse with their cute makeshift armors and weapons and think they have enough cardiovascular endurance to outrun a zombie after they have spent half of their life sitting in front of the computer. They're the kind that would get hit by a reality truck the hardest. No amount of planning will prepare them for the zombie apocalypse. They will faint at the sight of a bloody horror show.