RCM -effect

It's all depends on how much input credit that dealer is availed. As per your information, if all purchases are from the registered dealers then he would have Rs,18000 as  ITC. So the remaining amout of Rs. 3,600 should be paid through cash. If dealer purchases are puerly from Unregistered persons then he should pay Rs. 18000 Under RCM and he can avail the same as credit in the same month. The net impact is same in any case.

dealer can adjust the input CGST and SGST against the IGST laibility.