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. Just don't make that list 15 or 20 songs long.
Many DJs boast about the number of songs they have.
While variety is great, the fact is that they will only be able to play about 60 to 70 songs in a four hour show. Having the right 60 songs is a lot more important than having 1,000 songs your crowd doesn't want to hear. After you tell the DJ what type of party you are having and who the audience will be, ask them what type of music they'd suggest. You should feel comfortable with most of his or her selections. When it comes to a DJ's sound equipment, you probably won't know the difference between which brands are great and which are budget unless you are familiar with professional audio gear.