What should a person know before hiring a DJ?

This question is listed first because it is absolutely the most important one on this whole page.  Be sure you do your homework before you decide that all DJs are the same and you choose one based on price alone.  The best article I have ever read on the subject was written by my friend DJ Madman Mike.  
This article, "How to choose and hire a mobile DJ" can be found on Mike's website.

How much do you charge?

It depends.  A pro with years of experience, a huge music library, knowledge of all music genres, expensive professional equipment, talent as an announcer or master of ceremonies, etc. is going to be more expensive than a beginner.   Because of high demand,  Saturday events will be more than any other day of the week.  Some of the downtown hotels cost more because they are more difficult to get equipment in and out of and may require the DJ to hire an extra hand.   An event out of town will cost more than one in town.  An event that lasts 6 hours will cost more than one that lasts 4.  If you need extras, such as video services, more and bigger speakers, lights, etc. the cost can go a whole lot higher.   Our Party Train production retails for $3500.  But as a rule for a basic 4-5 hour performance, prices will range from about $400 on the low end to about $1000 on the high end depending on when, which, where, how long, etc.

How long will the DJ play music?

The length of time for the DJ to play is determined by the client when the DJ is booked and will appear on the written contract.

Will the DJ play longer than specified on the contract?

The DJ is not required to play longer than the time stated on the contract, but if the client wants the DJ to play longer, most will agree to stay an extra hour or two for $75-$100 per hour pro-rated.

Will the DJ play requests?

Our DJs will play as many requests as possible provided the specific DJ has the requested titles.   Each DJ brings his own collection of music and some have more music than others.

Will the DJ be playing any x-rated versions of songs?

As a general rule, we play only g-rated or clean versions.  We have edited radio versions of any songs which would contain any objectionable lyrics.   However, if a client wants the x-rated version, and the DJ has that version, he/she could choose to play it.  We aim to please.

Will the DJ smoke or drink alcoholic beverages while performing?

Our DJs will not smoke while performing, nor will they perform while intoxicated.

Will the DJ expect to receive a tip?

Tips are not expected, but are always appreciated.   

Will the DJ take breaks?

Our DJs play the entire time with no breaks.  But there are times when the music needs to be turned down or off for one reason or another.  We would stop playing for any of these reasons if requested by the client 

Are all DJs equally talented?

Obviously, all DJs are different.  Some are more talented than others.  Some have a greater knowledge of music than others.  Some have a better inclination for knowing what to play for a given crowd at a given moment.  Some DJs have a huge investment in the music they bring and some have a much smaller investment.  Talent, music investment, and knowledge are some of the factors that determine the price you are charged for the DJ you choose.

Are party guests allowed to set their drinks on the DJ's table, speakers, or other equipment?  Are they allowed to come behind the DJ's table and help play the music?  Are they welcome to come and look through all of the DJ's CDs?  Are they allowed to come up and grab the DJ's microphone at any time for any reason?  What if someone wants to use the mike to "sing-along" with the song being played?

Well, of course the answer to all of the above is NO.  Drinks are always a potential hazard when they are spilled on equipment.  We usually don't have a whole lot of space to work in, so anyone wanting to come behind our table would be in our way.  "Can I look through your CDs" is the number one thing to never ask a DJ, for so many obvious reasons.  Our mikes are available for making toasts, speeches, etc., but they are not made for karaoke.  Sometimes people have a tendency to scream into the mike which can cause an amplifier to blow up.