TAX on supplies to other state dealer

Dear Prem,

IGST is not applicable. The place of supply is dependent on 2 aspects - the location of the supplier and the place of supply as per section 10 of IGST (for goods).

Section 10 - Where goods terminate for delivery, i.e. Maharashtra. As supplier and place of supply is same state, CGST & SGST applicable.

Note: Karnataka dealer, cannot claim such credit (in KA) unless he is also registered in Maharastra. 

Yes, but you need to manually change the Place of Supply to Maharastra while filing GSTR-1.

Yes it could be possible. There requires to be 3 parties to the transaction. Bill-to Ship-to concept to be applied.