Our sorcerer got some officers to confront the person who stole his identity and we turned the human trafficking ring over to the guard who pulled everyone out relatively safely.
But to even things out the sorcerer killed someone for his cloak and my rogue stole stuff from a person we later found out leaves the thieves' guild the next session. Karmic balance.
More realistically the rank and file town guards will actually try as hard as they can to be helpful, because the medieval hue and cry system means every single one of them is a volunteer, meaning no millitary dropouts who want a paycheck and to feel like a badass.
Also in a city state set-up, they're more often than not also the millitary, so double on the no bootcamp dropouts point.
Where you'll run into trouble is more hierarchicalized cities where there's neighborhood and regional levels of overseership that can fall into the hands of corrupt officials who actively benefit from some criminal activities, more often than not in the form of bribes to look the other way, because again, all volunteer force, doesn't take a lot to be able to make participation worth more than the honor of the badge.
Hypothetically you could avoid this by making your police force all paladins and just constantly be checking for oathbreakers, but that's operating dangerously close to the "literally nobody would willingly subject themselves to this without pay" event horizon.
It doesn't really matter how you frame it, the existence of a police force is always going to necessitate power dynamics. Every form of policing exists to subjugate the public, from medieval guards who protect the crown to the modern day police force which is run by fascist gangs. There is zero context where you can go to an authority and not have to deal with those dynamics.
I mean maybe in real life. I had a game where one state was basically a commune. They had "guards" but they were volunteers from the community that were willing and able to do stuff like keep watch at night, make note of visitors, deescalate situations, and so on.
It worked well. The players helped stop counter revolutionaries from restoring the (now undead) despotic king to the throne.
Edit: there's power dynamics in any situation. This one didn't have authorities that were subjugating their people.
I mean we can basically justify the law keeping faction to act and respond in whatever way suits the story.
Perhaps the police are a mercenary company paid to guard the local clergy, so reporting their misdeeds is moot.
Perhaps as you said it's that the law keepers are an order of paladin's who must uphold their oath of enforcing the law or lose their magical connection.
Perhaps the closest to a guard force up to that point has been the ruling warlord's loyal warriors, and to your party, they're the enemy.
If the party become too over reliant or too wary of the police, have them reform in plot, for better or for worse.
More realistically the rank and file town guards will actually try as hard as they can to be helpful, because the medieval hue and cry system means every single one of them is a volunteer, meaning no millitary dropouts who want a paycheck and to feel like a badass.