Cst purchase is mandatary or not?????

There is no such mandatory clause for interstate purchases, it is purely your business decision. Some times we need to purchase material from outside the state bcoz of any reasons like...Less cost, good quality, Higher credit period etc.. 

  The cst paid goes to another state. That is the reason for not giving credit that tax paid on interstate purchases. When a local purchase is made once full tax had been paid to local govt on purchases. Hence,on the second transaction of the same goods a reduction is allowed......mjk  

  The cst paid goes to another state. That is the reason for not giving credit that tax paid on interstate purchases. When a local purchase is made once full tax had been paid to local govt on purchases. Hence,on the second transaction of the same goods a reduction is allowed......mjk