Agency can mean a number of things. Maybe we need to differentiate between being managed, having an assistant and agencies. I won't address pimping, that's pretty obvious.
Agencies: An individual who uses a central POC to allow hobbyists to schedule appointments. The agency advertises as such and has a stable (or coop) of willing participants. A hobbyist contacts the agency for whatever provider they'd like to see. The providers don't have their own handles or advertise on the site apart from the agency. The agency at no time pretends to be the provider but rather handles the admin of screening, setting appts, getting the incall, etc. and keeps the provider out of that part of the hobby. Of course the agency gets a finders fee, cut, or percentage of the rate agreed to by the provider. RGV GND and STF are good examples of this because their is never any doubt about the providers role or that of the agency.
Assistants: These are folks that work for the provider, usually for a flat fee or percentage. They are usually women (who may have been providers in the past) but some are men, gay friends often being utilized to help. The assistants also handle the admin part of providing, handling screening, questions(fucktards have so many questions), setting of appts, travel arrangements, writing of ads and showcases, etc. The best providers make this transparent and make it apparent that they are using an assistant in their ads (TheAlpha in SA for example). That way fucktards don't try to sext the gay assistant or otherwise get into some other mind fucking situation. At some point the assistant will pass you to the actual providers phone or message system. The provider maintains their own ECCIE account and never relinquishes control to another but may pass info from the PMs to the assistant. The downside is that fucktards are a skittish bunch and won't feel comfortable giving up any information to a third party. Some providers won't say they are using assistants though because of this.
Managed: This is usually manifested by an individual handling all aspects of a provider. This often includes exclusive access to the Verified Providers ECCIE, email, and phone accounts (sometimes the provider doesn't even know their own passwords). The manager will often pose as the provider in PMs, text and emails up to the point of a hobbyist meeting a provider. The hobbyist may be unaware that they aren't actually talking to the provider but may note some incongruities in conversations with the provider once they actually meet; i.e.
Hobbyist: So how was shopping?
Provider: What shopping?
H: You said you were shopping?
P: I was napping...
H:...
P...
H...
P: OH YEAH, shopping, it was, um, great!
The manager handles all specials, ads, etc. This may be attractive to some providers since they just have to show up, play, get paid and leave, only dealing with fucktard nonsense during the session, insulated from all of the silly questions, texts and fucktard BS. Since all of this happens behind the scenes, some hobbyists will feel that they were duped into sharing personal info and possibly some intimacy with a third party without their knowledge. This can be unsettling to some fucktards based on their RW situation and the aforementioned skittishness some possess.
We have noted that some in CC may have actually been a combination of Agency and Managed and seems to have caused the most consternation of those in the CC community. I think this was how the now defunct HenHouse may have been operating, not really as an agency per se, but rather as a hybrid of manager and agency. I have no inside information, just a theory.
My 2¢.
Thoughts?