In some cases, the event organizer provides its own official resale shop. Customers can offer their tickets for resale in this shop.
This shop offers 100% protection for both you and the buyer. If a ticket is sold or purchased through the resale shop, this is not considered black market trading.
You can check whether the event organizer has enabled the resale option in your MyTicket portal. The option is called "Resell".
The button shown in the picture is visible when a resale shop is available: