Never be afraid to ask questions. Ask for references. If they don't have any, ask about their experience. Feel free to ask why they got into the business. What motivates them to do a great job for you. If the answer is "money", you might want to interview others. Yes, money can be a great motivator but it should never be the main reason.
The better you know them, the better your event will be. Less stress on you equals more fun overall. Take your time and find just the right one.