The laptops and machines I have avaiable are initially listed on Facebook Marketplace. I only sell the machines locally -- to avoid scams, the delivery/packaging hassle, and to more easily deal with and honor the 1-year hardware warranty. And I take my time with each machine... so I do not have large quantities to ship all over the place :-)
From Marketplace I generate a "spec sheet" that is displayed with the units, and also here on the Erwin Computer website. It makes things very simple and consistent.