I have a .com domain name that expires in 2021. I've only used it a couple of times and am researching how difficult it is to sell it. A quick check indicates it might be worth about $600. Currently it is registered at GoDaddy. They will let me list it for sale for $4.95 and take 20% of the sales price if it sells. They ensure the seller is legit, etc. No idea if they do any "marketing" or how folks know GoDaddy has domain names for sale. I see other places listed on the internet like Sedo, Flippa and Afternic but haven't researched them yet.