It is always good to have something in writing from the person doing your makeup that confirms date, timing of service, and fees. When hiring an artist several months in advance, ask about what they do as a backup situation if they are unable to fulfill their contracted service- is your deposit refundable? Book with a reputable person. The best recommendation is always by word of mouth. Using a makeup artist that has done people you know or recommended by your vendors is always a better choice than going with an unknown.