Set off

can i take vat purchase as set off agst cst sales

no, set off only against vat sales. Because vat relates to state where as cst relates to central govt.,

yes u can claimed vat paid  ( purchase withing maharashtra ) against  cst payable  (oms  sales ).

u can't claimed set-off of cst paid on purchase out of maharashtra against cst payable on oms sale as while purchasing goods from other state, u r passing taxes to that other state & not to maharashtra state & hence, maharashtra vat rules don't give u the credit of the cst paid while purchasing from other state.