Reverse charge

if you have purchased above rs.5000/ reverse charge applicable to you and the unregistered dealer provide you Bill of supply instead of Tax invoice

if you are not registered in Varanasi than he cannot sell goods to you.....either he has to register in Varanasi or you have to register there....otherwise you will not be allowed to cross state boarder with the material....even if you did in any way it will be illegal.

as far as invoicing is considered for rcm transaction, you shall issue an invoice like you issue for any sale and instead of writing your customer name write your own name and gstin number and mention in invoice that tax is to be paid on rcm basis....