Choosing a DJ can be discouraging; especially if it's your first time.
Here are some tips to help you avoid a negative experience.
Once you have a list of DJs, talk to them. Pay close attention to their professionalism on the phone.
Your event will most likely require music to satisfy all ages and musical tastes, so ask about variety and policy on requests. Professional DJs read the crowd and play music that keeps the dance floor full. They don't just play what they like and want to hear.
Get the details about equipment. A professional DJ should have professional sound equipment; not "home consumer" gear.
Ask when they will set up and do a sound check. Professional DJs will be set up well before your guests arrive.
For wedding receptions, a good DJ will take the time to explain how they will handle the details of the introductions, the first dance, bouquet/garter and special requested dances. They will be able to communicate well with you; should be willing to listen to your ideas and meet any special requirements.
Your DJ should be familiar with most of the music you want and should know how to organize the event within your guidelines. Try to determine if your DJ has the ability and willingness to "read" and motivate the crowd.
Beware of any DJ who is so eager for your money that he/she allows you to program your own dance by accepting a long list of music from you. Professional DJs read the crowd and play the hits that work best for the crowd that night. Your personal favorites may not be what works best for your crowd. For your own sake you should let the DJ do what he/she does best.
Professional DJs will not try to be the "life of the party".
Professional DJs will not invite potential clients to watch them perform at your event. A DJ cannot give your event 100% attention if they're trying to sell to other clients.
Professional DJs will use contracts, to protect both themselves and you.
Last, but not least: what is the price? You have to ask yourself if the average price for a DJ is $450 and if a DJ will undercut or quote you $300 for the job, why is he/she so willing to charge so much less? DJs are not all created equal!