Go with your gut when hiring a disc jockey. If they don't come across as professional, or you simply don't develop a rapport with them in person or on the phone, choose someone else. You may be noticing something on a subconscious level that could affect your event.
When looking to have music at your next party, consider bringing in a disc jockey. These people will have or have access to a wide variety of music and can even provide their own equipment. Check to see if they can provide the type of music that you want from their performance.