Not all agents are created equal. There are no qualifications required to be an agent, no certification board to which one must submit. Thus, technically, anyone can call themselves an agent. Doesn't mean they *should*... but they *can*.
As an author, it's key to do your research and know the difference between a good agent and bad. There are red flags you can look out for, and due diligence you can do to protect yourself.
It is better to have NO agent, than a BAD agent. So how can you tell the difference between a good and bad agent?
First thing is first: MONEY SHOULD ALWAYS FLOW TO THE AUTHOR.
Number one rule. If an agent or agency asks you for money upfront, RUN. It's a scam.
Beyond this, there are many insidious and less obvious ways in which an agent can be shady and/or "bad" (on a relative scale), and there are some things to look for/consider:
What is the agent's publishing experience/credentials for agenting? Anyone can hang a shingle and call themselves an agent, but that doesn't make them qualified. An agent/agency should have concrete publishing experience, ideally: full time jobs in the industry held over a number of years, including but not limited to being an editor, publicist/marketer, assistant, etc. at a reputable publisher; working at a reputable literary agency with strong sales; working as a bookseller; having interned at an agency IN COMBINATION with one of these other things. Someone who interned for a little while and then started an agency likely doesn't have the experience and contacts needed, but if they interned AND worked full time as an agency assistant for, say, two years, they may have the chops.
Quality of experience does matter--look at where they worked. Publishing is ALL about connections and networking, and thus where you have "walked" matters for where you will land.
Everyone has to start somewhere, but... Every agent is new at some point, but what's the distinction between someone who is new and bound for a robust and successful agenting career and a schmagent who won't be able to do much for you?
Look for the intersection between what agency they're are with coupled with their experience. You need either an established, reputable agent to guide you OR lots of industry experience (or both, but at least one)... thus a new agent at an established agency is a safer bet than a new agent as a dodgy agency with limited sales. A new agent setting up a boutique firm with lots of industry experience is a safer bet than one with little to none.
Look at their sales record You can look up sales on Publisher's Marketplace (with either a subscription OR if they have a free profile page), in Publisher's Weekly (not representative of all deals)... look on their website who their clients are and where their books have sold. Here is where the agency can really matter: a new agent without a sales record but at a reputable agency with strong sales? That agent is likely a safe bet. Newer agents at established agencies receive mentorship/guidance, so you can usually look at the agency's representative sales/client record and get a good sense of how they are.
BUT agencies/agents widely range in terms of where they make sales. Pay attention to things such as:
Do they primarily make sales to publishers that don't require agented submissions?
Have they made ANY sales to Big Five/major traditional publishers?
Where do you want to be published, and do they have the connections to make that happen?
The thing with agencies that primarily sell to small publishers with open submission policies and/or digital only publishers, is you have to ask yourself: what can they do for you that you couldn't do for yourself? Do they have the relationships to make sales at major publishers?
Often bad agent and schmagent are used interchangeably, but there is a special type of schmagent worth noting: the well-meaning agent who just can't make the sales you want.
Many schmagents mean well. They hustle. Many have excellent social media presence and are VERY nice.
But they have middling to no ability to sell your book to the publishers you want them to sell it to (if you want a mid-sized to large traditional publishing deal). Look at their experience, their sales--delve beyond social media presence and an attractive website. Is this agent representing authors successfully and selling their books to major, reputable publishers?
To my mind, a schmagent is someone who has been around a long time--many of them have splashy social media presences (and participate in the online contests)--but you never seem to see any sales from them, ever. Or if you do, it's a sale to a publisher that accepts unagented submissions. They just don't have the relationships, connections, "eye" and/or taste level to get things read & sold. And/or there is SOMETHING going on below the surface that we, the writers, can't see that must be impeding their professional progress (personality issues? writes terrible emails/pitches? editors just don't like them?).
As an author, the key is to do your research. And never query someone you wouldn't be happy to accept an offer of representation from. If they're not making sales to the types of places where you want to be published, don't query them.

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#HowToAuthor: Agents & Submission
Non-FictionAdvice for writing book-shaped things and getting them traditionally published. This series will cover everything from querying to agent fit, to building a platform and marketing yourself.