As I've previously hinted, music supervisors do have an inherent interest in the agencies that represent independent artists. There are quite a bit of sharks in the licensing waters, partly because it's the music business (see Hunter Thompson's co-opted quote on the matter) and partly because it's where the music money is located these days.

Anecdotally, I heard via a supervisor about one agent recently blacklisted due, in part, to what was deemed an unethical fee submission policy. Further, major network studios have begun vetting library music companies as the inherent lack of proper clearance or shady dealings among newly sprung companies has become a serious liability concern.

Very good, well-used and well run agencies tend to have similar identifiers. I've done business with a few of these agencies via music supervision I've done, or have heard the same agency names consistently mentioned by the supervisors I do business with. And further, I like to think I practice the same policies and concerns.

So a few signs in spotting reputable licensing agencies (or "song pluggers" in the parlance of olden days):

No submission fees.
A successful agency will not charge a fee in order to simply listen to submitted music.

No re-titling.
I don't know of any popular and regularly used agent that re-titles its catalogue for additional publishing income purposes.

Takes a commission only from music placed.
Some agent agreements ask artists to sign away rights to fees for any sync placements whatsoever. Agents do, however, have to eat, pay the phone bill and buy cat food, and percentages do vary. But earned percentages--and only percentages--are industry standard.

A list of placements.
Agents tend to post most if not all placements they've done on their websites. If you don't see any list at all, or general logos of companies they claim to do business with, or an inordinate amount of MTV usages (which rarely pay substantial licensing fees), it's likely the agency is making money elsewhere, more than likely at the artist's expense.

For a talented artist with licensable music, finding a good agent that fits should be relatively easy and stress free if the research is done; the above points can usually be sussed out quickly from an agent's website alone. And not all agencies doing business differently than the above are evil or cheat the artist. But read the fine print and remember Thompson's sentiments.