They then choose the most qualified people to introduce them to their company's hiring manager. Recruiting agencies are outside firms that seek candidates for employers. Don't confuse recruitment agencies with employment agencies. The main difference is who ends up being your employer.
Agencies are paid to fill positions, not to book interviews. You're likely to get fewer candidates, but each one will be qualified. As a recruiter and then as a branch manager of a recruitment agency, I knew my clients well. Not only were they telling me the skills required, but over time I learned who would be a good fit and who wouldn't.
It's best to avoid this situation if you can and avoid any agency you catch lying about their status as a preferred provider. They use recruitment agencies to do this for them, so that the employer can spend more time interviewing candidates. It's the agency's responsibility to find your next great employee in their area of expertise, and that's why you're counting on them to hire your next best employee. After using these interviews to further reduce the number of candidates, your company will receive information about each candidate and the agency will help you organize the final interviews.
Temporarily or temporarily to permanently These agencies send temporary workers who can come and go or, if you think they are a good fit, they can transfer them to your payroll. Once an agency has done this with your resume, it can be very difficult to get those employers to consult it, since the employer has not agreed on payment terms with the agency and does not want the hassle of an aggressive agency trying to bill money that the employer has not agreed to pay. There are employment agencies that provide IT support staff to companies, but professional engineering functions are usually found through recruitment agencies. From the employer's point of view, employers generally don't like agencies that send them unsolicited or inappropriate requests (known as “paperwork CVs”).
A recruitment agency to find the right candidates (not just a group of candidates) may be the best option when you want to get the most out of your money. Some agencies are paid at a fixed rate and others are paid a rate based on their starting salary. If you're not satisfied with what you find, there are usually other agencies that advertise the same or similar position. Unlike most employers, who only have access to LinkedIn, recruitment agencies use multiple sources, including their own platforms, in many cases to attract as much of the best talent as possible.
A recruitment agency can help lighten the selection burden, so you can only focus on the most qualified candidates. If the agency is a preferred provider, that means that they have already agreed on payment terms with the employer and the employer will consider your request. Unless you hire a boutique recruitment firm and save yourself all the stress and frustration of hiring the wrong tech candidate. I recommend verifying that the agency is a member of The Recruitment & Employment Confederation, the only recognized commercial body in the industry for recruitment agencies.