If you've tried everything you can think of to land a literary agent to represent your work to publishers, you've probably failed. Through no fault, necessarily, of your own.
Welcome to the Real World of book publishing. You know, the one where landing a publishing contract is only the second most challenging thing for a writer to do; landing an agency contract is number one. Far and away.
The reason is simple mathematics. Sure, for every book published, probably a few hundred or more go unpublished. But for every agent landed, thousands of authors get turned down. The reason is that there are only so many agents to go around, and they're in huge demand. That's because good agents can offer fledgling writers invaluable advice, so they act as sounding boards and dispensers of knowledge. As a result, book publishers increasingly turn to agents to "screen" the work submitted to them in order to save their editors time. Agents weed out the junk (or the vast majority of it) and pass along only the best of the works they receive from their represented writers.
The problem comes in when you stop to consider that an agent can represent only a few authors efficiently, considering the amount of time each writer requires of the agent. So, when an agent's stable is full, out go the turn-down slips. Even if an author presents precisely what that agent has been lusting after for the past twenty years, if there's no room at the inn, Mary and Joseph have to look elsewhere for a place to crash. See my point?
I know. It's not fair. And it's certainly not encouraging.
But, with that said, really good writers with marketable properties will eventually rise to the surface, and if they're persistent in pursuing leads about which agents are currently looking for new clients and which aren't, they'll eventually get signed up. I've had my present agent for twenty years, and she is simply the hardest working, most honest, most fairt, and most knowledgeable agent I've ever had. And I had two others who were also top-notch, both of whom are, uhh, no longer taking clients. Or breaths of air, if you get my drift.
In between those three, I had three others who were the absolute pits. I fired them all for non-performance, losing several years' worth of time in the process.
Things like that happen. But, before worrying about something similar happening to you, worry about becoming the best writer you can be; read everything there is to read about agents and what they want and how they want to be approached, and go from there.
Be diligent, but don't be obnoxious. A little honey will go a long way toward finding you a new hive in which to rest your stinger.
Oh, and by the way, legitimate (or, as you put it, "true") agents don't charge their writers for anything other than the commission they collect from the sales they make. But they do bend over backward to help their writers improve their works and increase their chances for publication.
Trust me on that. You're listening to the voice of reason here. Either embrace it or perish!
Okay, nothing quite that dramatic, but I do speak from my own experience, which is something I wish someone would have done for me when I was starting out as a novelist.