CST amount collection in lieu of C-form

if the goods are sold at zero rate or at reduced rate in case of inter state trade a declaration form should be obtained from the party which is required to be produced before the assessing officer at the time of assessment as a proof of such zero rated or reduced rated sale. now in the present situation all the bills were despatched charging no CST. and the customers are now willing to make payment of the CST amount instead of providing the C form. now at the time of the assessment the C form will have to be produced to claim the zero rated sale. but as u will not be able to  provide the same the tax authority will impose the tax rate which ought to have been imposed if it was not a zero rated sale i.e. 12.5%. so u will have to provide this from uor pocket. now what u can do is to charge the whole amount of such CST to the customer.  moreover as u have not deposited CST for the whole year. hence the tax authority will impose interest on that. the returns were also made defective showing no CST there. for that penalty may also be imposed. so having regards to taht u should charge all that amount to that customer. now it will be better to have a discussion with the sales tax authority how the matter should be resolved.

Please enligten us on the following topic. We are power equipment manufacturers located in salex tax free zone where CST is exempted against submission of form -C i,e zero tax or else it will be charged @ 12.5%. In 2006 April we have supplied machines charging nil CST against form -C.   But, till date C-form is not recd from our customer and now  they are willing to pay CST amount.  How much amount we have to collect ?...is there any interest + penalty?  Please also let us  know after receiving the amount  what documents we have provide to the customer? Is it proof of CST paid challen or any invoice to be raised.  Please suggest.

Thanks & regards

Sharan