Ask about how long the maids have been working for the company. Many of these companies have a very high turn over rate in staff which may indicate they are not paying well or not selectively choosing staff. Companies with a stable employee base are usually the best possible option for a maid service both in security as well as high levels of professionalism.
Selecting the right maid for your needs is a personal decision. For each person, the cleanliness for their home is really up to them. If you will hire a maid to live in your home and handle the day to day cleaning, you will pay more than a maid that will come to your home several times per week. Nevertheless, the type of cleaning you need is yours to decide.