An agency or co-ordinator should represent models. The model must have a portfolio, and comp cards. The agency/coordinator provides you with work (That is their main purpose. It is safe to say that they work for you!) They make a commission on your fee (15 to 20%). Be warned about agencies/coordinators who ask for money up front! Also check to see if they are reputable and genuine. The agency/coordinator should provide you with a few photographers name. It's your choice to get the photographer you want. Pay the photographer for the photo shoots not the agency/coordinator. The agency/coordinator provides you with safe working environment and looks after legalities of the paper work for the job. They provide their clients with "Professional" models. Keep copies of all-important papers, such as contracts etc. You may need these if you have a dispute with the agency/coordinator. It is wise to choose the agency/coordinator carefully so you can stay with that them. Constantly changing them gives you a reputation of being flighty and unprofessional