I am not sure if it is a good idea to hire through firms that charge the candidates. I understand you want to reduce your costs. However, such agencies have been known to indulge in bad practices which can adversely affect the quality of employees and, in some cases, be dishonest. Most employers are willing to pay recruitment fees for services that the placement companies provide, and for a reason. Just think... if you were looking for a job, would you be willing to pay to get the job? You would if you were perceived as undesirable. Is that the type of employee you want to hire? Is that the person you would trust with an expensive car to handle?
I do not know which sites you are exploring, but if you are searching for drivers and housekeeping staff, what percentage of them will be using the internet? Outsourcing agencies may be a better option for you. You may end up paying around 10% more, but it is generally a more reliable choice.
Best regards