Net profit of retailer

Dear All,

  A retailer purchases from a wholesaler products with gst tax invoice

if the retailer sells the same product to end customer without gst tax invoice(kacha bill) then will he get full profit?

selling price minus gross purchase amount(amount before purchase gst) or will his profit be selling price minus net purchase amount(purchase amount plus purchase gst amount)

Also if a retailer purchases his goods in cash from a wholesaler who gives him kacha bill,can the retailer show sales of such goods in his books of accounts,or will he has to sell it without issuing any tax invoice.