They do NOT provide printed detailed price sheets. ASK for one and a detailed and itemized bill before you sign. Do NOT believe claims to erase pictures within 24 hours.
They add on extras (expensive paper, additional people in the shot, retouching) and do NOT let you know your options unless you ask for a break down. Know what you will be charged for before you sit down in the make-up chair. Use a credit card or Amex so you can stop payment if there is a dispute. Ask question first, get in writing and then come back. Ask to see photographers work. Speak up about make-up/hair preferences.
Tip: Original digital images files can be purchased for $100 per pose on CD so you can retouch them yourself at home with software and own the copyright so you can make your own copies.
Pros: Accessible, Silly and fun, Can be economical
Cons: No printed prices, High Pressure Tactics, Must be wary