It is completely free to list and to use Warrp in general. The only time a fee is incurred is when the Safe Escrow facility is used to complete a transaction, i.e. when both the buyer and the seller taps on the Finalise Transaction...

  Safe Escrow is an optional feature provided to both buyers and sellers to ensure that a transaction is conducted at the highest level of protection and fairness.     How this works At anytime after a Buy Offer...