Undelivered items will undergo a Quality Check (QC) session and if suitable to be re-sold, they will be returned to you.
See here for further details on returned items.
If the items don't pass our QC, they will be bought by "RedMart" that will act as your customer in this case. We are going to pay for the items at the retail price "discounted" of the RM commission.
See here for further details on the invoicing of undelivered items.