"Remember that money flows TOWARD the writer," says Science Fiction writer James D. MacDonald. It's a pretty good rule of thumb that anyone in publishing who asks for money from a writer is a bottom feeder who is taking advantage of the writer. There are things a legitimate agent may bill to a writer -- but that is paid only after the agent makes money FOR the writer.
Register for free browsing priviledges at the Literary Market Place (website listed in the resources at the bottom of this page). The LMP is a long standing business registration reference book for the publishing industry. While they won't give you individual names without an expensive subscription, you can click on their "Alphabetical Listing of Literary Agencies" to see if the agency is listed there at all. Listing in the LMP does not guarantee legitimacy, but they don't list outright crooks.
Check out Preditors and Editors, a website listed in the resources at the bottom of this article. This is a site that keeps track of reports of good and bad behavior of various agents and publishers. They have listings for a full range of agents from crooks to agents who don't answer phone calls to the best in the world.
Check out professional writer's organizations, like the Science Fiction Writers of America, The Society of Children's Bookwriters and Illustrators, and Mystery Writers of America. Many of these organizations have "affiliate memberships" for unpublished writers, and all of them have resources to help find honest agents and publishers.
Lastly, if you can't find good information about this agency from any of these legitimate sources, tread carefully. Watch out in particular for any agent who won't tell you who his or her clients are. Also run the other way fast from any agent who sets you up with a "book doctor" or an "independent" editor or producer who will fix your book for a charge. The most dangerous can be those who claim they've set up a big money deal for you, but won't tell you who the buyer is until after you sign a contact. (The contract is almost always full of fine print guaranteeing you will pay them money for something or other.)
There are legitimate book doctors out there, but they generally don't need to partner up with unknown agents to get clients.