@Zoey > The CDJ800 was continued for no other reason only that they were replaced by a newer generation of CDJ so Pioneer ceased making them any more. The reliability and quality of the deck generally commands a good price for second hand gear.
However, all second hand gear can have its problems and, just like a car, the CDJ may need to be serviced if its not performing 100% (laser re-alignment etc). This would be fairly rare though.
If you want to use just a laptop as your music source then perhaps you should consider a controller.
If you want to use multiple music sources then consider some of the newer technology available such as the 350s / 850s etc which can mix music from your laptop with software or use CDs / USB sticks.