You need to list with a recruiter that works with your field. A recruiting firm, unlike an employment agency, works for a company or corporation. The hiring company pays the recruiting fees. If a recruiter asks you for payment, you might want to move on. The exception to this would be if the recruiting firm is going to perform a service for you, such as preparing a complete resume package.
Lets start at the beginning of the process, from the perspective of a recruiter, with the resume.
The resume is your marketing tool. Most people cannot write a resume but are convinced they have a work of art. Professionals work long and hard at perfecting this task. If a recruiter calls asking questions and clarifying information its because the resume, in their opinion, isn't going to do the job at the company level. The recruiter is going to need answers to questions that the company is going to ask and MUST be answered.