You MUST succeed if you follow these guidelines, because people who do more than what's expected of them always do. Just remember to be specific, persistent and flexible. The best they could do is try to talk you into an interview you are not sure about. If you are confident and sure of your goals, they are an excellent resource. The cost is nothing to you and many organizations use these entities for all their hiring.
Most organizations work with niche groups.
Some will not even work with you unless you require a six digit income. Others specialize in technical positions. And then, of course, you have the ones that focus on clerical placement. What you must do first is figure out exactly what it is you want and need in a job. These parameters might be very narrow or somewhat wide.