As a DJ you have several hustles. There is DJ'ing the party. This is always a risk because you are bringing thousands of dollars of equipment with you. Most theft is done in the form of a few records here and there or a cord or two.
Wedding DJ's are worse. No matter what formula you have for a successful gig, you will always have a drunk relative that feels the need to MC, a demanding bride that gives you a list of music she DOESN'T want to hear and a group of people that will always request music that you wish was never written. for me that is ANY slide. I hate weddings.
Getting a residency at a club is better but you still have the other DJ's to worry about. They WILL steal your music given the chance. When you work this way you also have to worry about not getting paid. You are the lowest employee in the club. The owner will pay the bouncers, bartenders and even the guy that sits in the bathroom before he pays the DJ. He feels that he can ALWAYS replace a DJ.
Then there is selling mixes. As a DJ you are trying to sell your best sets. You figure youput that set together better than anyone else could have and you have fans that feel the same. Sometimes these same fans bring these CD's to parties with them and try to get the DJ present to play them. Oh, joy.
If you get good at the party mix you can put those CD's in stores. It is not easy work and you always have to worry about the idiot that tries to undercut you. There is ALWAYS an idiot trying to undercut you whether it's at a party or selling your mixes. Even if you become successful with your mixes and you go to collect your money the owner of the shop will always hit you with the fact that some other idiot is selling his mixes for less and you should do the same (see DJ Apollo for the reference). The whole life of a DJ is very cutthroat. Still it's is better than having to clock in for some faceless corporation that feels it should replace you every 6 months.