This is unfortunate because it is frequently a last resort for employers. Advantages of classified ads are that they list specific openings and have frequent new listings. They are widely viewed as ineffective, primarily offering low paying, low status jobs. Their main advantage is that there is no cost to the client or employer. Depending on the agency and the position offered, the fee may be paid entirely by the employer or by the employee, or they may split it.
Some agencies specialize in a particular field such as clerical workers or sales people.
Private agencies tend to be more successful with experienced people with sharply defined skills, good work histories, and employment in a single field. Advantages are that they offer a chance for employer and prospective employee to explore the possibility of a permanent relationship and they may list positions not offered elsewhere. The main disadvantage is the fee. Once you have found a job that sounds good to you, you must apply for it. This involves writing to the company offering the job and including your resume or a job application.