Registrar is the latest to add functionality to sell domains.

Dynadot lets customers negotiate domain sales through its new system.
Domain name registrar Dynadot has debuted a new system to help domain name investors sell their domains.
The company allows registrants to add for-sale landers to their pages and to negotiate sales from within their registrar account.
Dynadot handles the payment and transfer into the buyer’s Dynadot account. It charges a 5% fee if payments are received in account credit and a 10% fee otherwise.
You can see an example of a Dynadot for sale lander at Dynadot.uk.
Dynadot is one of many registrars now offering for-sale landers and systems that make it easier for their customers to sell domain names. PorkBun is charging 7% for transactions on its landing pages that include fun, TLD-customized landers. .Sav.com also has landers with a 4% fee.
I recently interviewed Dynadot founder Todd Han for a podcast that will be published in the next few weeks.