How to choose your wedding day hair stylist and make up artist:
Get in writing that the person who performed your trial session will be the person on site the day of your wedding.
Qualify your stylist that they understand the difference between everyday make up application and make up for photography and they have experience working with brides. If they have never done make up for photography keep looking for someone who has. Your wedding day shouldn't be the day they begin experimenting with new techniques.
Make sure your up do is securely fastened and is going to last the length of your reception. Also take a close look at how your hair is fastened after your trial session. This is important if you don't want a lot of exposed bobby pins.
Clarify if they will be bringing an assistant(s) on your wedding day.
Ask for a contract in writing guaranteeing their arrival time, date of your event, services to be provided and cost for their services.