Turntables are divided into two groups: belt drive and direct drive. Usually belt drive turntables are for beginners that don't want to spend a lot in a turntable. The platter (circular section where you place the record) is connected to the motor with a belt. They do a good job for basic mixing and record playing but not for scratching where the DJ is stoping and starting the record all the time
A direct drive turntable has the platter connected directly to the motor giving it more strength. The higher the price of the turntable the higher the torque and power of the motor. Low range turntables have a torque of about 1 kg, a medium range turntable have a torque between 1 and 2 kg and high end turntables have between 2 and 5 kg of torque.
Another factor to consider is the shape of the tone-arm. Usually straight tone arms are less prone to skipping while s shaped tone arms can offer better sound quality.
If you are considering focusing your DJ performance at scratching it would be wise to spend a little more and buy a mid to high end turntable. On the long run it would be a better investment. High end turntable, if taken care of correctly, can last many years.
Phono Turntable cartridges
Upgrading your turntable cartridges carts can imporve ina big way the quality of the audio and your scratching and mixing performance.
There are different cartridges designed to specific DJ styles. For example the Shure M447 is excellent for DJ scratching and Ortofon Elektro is supreme for electronic and dance music(tipically in discotheques and dance clubs).
Cartridges include needles but turntable needles can also be bought as replacement part for turntable cartridges. Needles, as anything mechanical, wear out. A wear turntable needle can damage a record when playing so it is wise to keep your turntable needles in excellent shape the play records . Any time you replace your turntable needles you would need to re balance your turntable and adjust it. Please follow the manufacturers instructions for re balancing your DJ turntable.
As a general rule of thumb hange needles every 500 hours if you mix and more frequently if you scratch. Keep them clean and also keep you records as clan as possible.
Usually same manufacturer needles will fit the same cartidge manufacturer. For example Shure needles will fit with out a problem Shure cartridges but you will get the performance of the weakest link. In other words if you fir a top of the line cartridge with a low end turntable needle, you will only get the performance of the cheap turntable needle.