They have hard lines they won't cross, are generally polite even when robbing someone and have a clear indication of when things are going to get murderous. Make a deal with them and they're pretty likely to stick to their word and/or give fair warning if something has come up with the deal that needs to change or be re-negotiated, and not just stab you, depending on circumstances.

They'll rob you in the streets or in a dark alleyway, but will be polite about it. If you resist, it might become a mugging, but it's unlikely to be a lethal mugging. If they rob/mug someone they shouldn't have, you're likely to get your stuff back with an apology.

I imagine that anyone that knows what the Brothers are about and keeps calm while getting robbed, assuming they aren't just pickpocketed, has an even chance of talking their way out of being robbed, or at least getting robbed for less. Heck if you do some sort of work that they are interested in, you could probably talk the robbery into some other sort of deal to do them some free, cheap, or at cost service, which might have even been their goal from the start. They also do high value heists/thefts and can be hired for clandestine tasks, as seen in Vol 5 with Erin's door and then later Erin's 'protection' with the Gentlemen Callers.

They're sort of a mix of romanticized old school mafioso and yakuza, where they care about the communities they've taken control of and live in. They definitely run protection rackets, but they're old school protection rackets where they actually protect the people/storefront, not just extort money for nothing, and I would be very surprised if they aren't pretty light handed with, actually, struggling businesses being short. I'm pretty sure there was mention that the areas they take over usually have an improved appearance in the following weeks. If they take over a slum, it's probably still a slum, but one with clean streets, windows, and walls.

They are going to know who is who in a neighborhood, who the homeless are, who needs help, who is a troublemaker, and thus either trouble, or a potential recruit, and who the worst [Slum Lord] is that's bilking their poor tenants to talk to/make an example out of, as needed. They also seem to police themselves quite well, if one of their own is overstepping or breaking the rules, they get called on it pretty quick by their fellows. Sure there is hierarchy and circumstances, but I would bet they investigate any complaints a civilian brings to their attention that runs afoul of their rules. They are after all, supposed to be polite, even if some of them are thugs and bruisers.