These ^ are called scabs, preying on the dreams of people hoping to go somewhere. $7500 bucks and 50 percent. They are fucking nuts. You could do some pretty heavy promotions for yourself with that kind of cash and pocket all the gig money DIY'ing.
The reality is you have to build your act to the point where legitimate PR reps, who actually have real industry connections, and actual legit booking agents, approach you because you have done the legwork to raise your profile to the point where they think you will generate income for them. Even then, the number of gigs available is limited with many bands clawing to get them, and the legitimate agents out there often already have full rosters and aren't going to risk an unknown unless one of their acts quits, gets sick, or dies. And even then, in a lot of cases, by that point there it may just make you more $$$ to continue to do it yourself.
The only real benefit is some of those agencies will have circuits locked up, and you are locked out, save for last minute cancellations the agency isn't available to fill. I had a real problem with that in central FL since Tom White/Skipper's Smokehouse basically runs the entire central Florida blues circuit. His bands get first crack at the best gigs, and I was left to pick up the scraps. He didn't need any more artists on his roster. This is one big reason I relocated to a place where there are just more gigs I can get on my own, period. Even so I worked with a scab agent for a time here because it benefited me FOR A TIME. As soon as the gigs I wanted to take folded I quit taking gigs from that person. That person takes fifteen percent but also tries to hijack bands for a percentage of tips, the mark of a grifter. I wasn't born yesterday so that dog didn't hunt and she knew it, but she tries pulling that with young, ignorant, desperate people.
Good luck out there brother.