Just keep in mind, as you search, above all, you want your event to be fun and memorable. These are all good clues to the DJ's skills and personality. Always ask the DJ about their policy on requests. The best DJs will take requests from the audience and work them into their routine. However, do not expect the DJ to play every request.
Many requests are simply inappropriate for the mood of the event.
A good DJ is not a jukebox. He or she will blend requests with songs he or she feels will properly motivate the crowd. Instinctual timing is critical in the art of DJ'ing and this takes experience. On the other hand, the DJ should try to play as many of your audience's requests as possible. Try to get a feel for their philosophy of requests as you interview them.