Oh yeah, I always wondered about those kinds of gangs/cartels that barely even try to hide. Could one just walk in and place an "order"? Seems pretty risky, even if they agree, you might end up owing them (or rather, being owned by them) forever.
I live in a country with extensive cartel activity, and can safely tell you that there's no need for them to hire specialized assassins from some shadowy international network. Instead, they simply use their own psychopathic people to get the job done as requested. Quality of killer (or group of killers) will depend entirely on how difficult the target is. The cartels have MANY members, direct members, who can be found for jobs of variable difficulty: a few random jacked up sicarios to spray a bar full of people where some low-level target who pissed them off is drinking, or for more protected targets in higher-level settings, a couple of ex military or ex police types (also very often employed by cartels as active members) who know how to use weapons well and with more subtlety, and target someone after some careful surveillance. Both happen often and sometimes a mix of the two kinds of killers is used, or other methods such as explosives..
Furthermore, nobody in their right mind would try to use such a favor against their cartel bosses as leverage. The police would likely never touch the case or care about it at all and the cartel bosses are in any case usually well known in ways that make new accusations of murder irrelevant, and very easily capable of butchering whichever random hired killer did indeed try to threaten them somehow.
Damn, I'm from ex-USSR but even we never had this kind of stuff (Russia did, however).
Bribes, intimidation and murder happened quite often (and still does), but it's hidden, few dare to do it out in the open, in broad daylight and/or with rifles/explosives.
Silver lining of the police being the biggest gang, heh.