purchase from unregistered dealer

I think u can't take benefit of input tax credit and u have to pay full gst of your sale. for example:-
any product u buy R's.90. and gst on the product is18% and your margin is R's 10. then your tax invoice total value will b rs118. ur gst liability will b R's 18.
as per my knowledge I explain u if I m wrong please tell me.

case 1 purchase from unregistered dealer
u hav to pay gst under reverse charge and u will get itc of that while discharging ur output tax

case 2 purchase from composite dealer
u wont get any otc on this purchase and py full tax on output supply