Flippa is a good place to sell, but it will cost you to list your domain, you can buy them there as well. I like auction sites like GoDaddy can find some gems. Also there software you can purchase to find expired ones as well
I agree that Sedo is a good place for selling domains. It's easy to use, and it also has an affiliate program, so when you drive traffic to your listing and somebody then buys something else, you earn a commission. That's nice!
Sedo usually works better for domains that are more on the higher end of prices. That's not always the case but overall that's what works best on Sedo. Flippa is a good one for medium to lower end priced domains.
Godaddy is good too - not sure about their conditions though, and what it takes to have your domain listed there. I think there's some kind of membership you need for that (though it's not expensive). Also not sure about their affiliate program. They've changed it quite a while ago, and I have no idea how it works with respect to domain sales.
Yes, GoDaddy requires a membership to list your domains for sale there. I haven't listed anything there in a while but the main condition that used to stand out to me and other domain investors is that you can not list domains that will expire in 90 days or less.
Sedo is a great place to trade and sell domains online. However I have some good experience of selling my few domains from Digitalpoint forum marketplace. If you have registered your domains from Godaddy or namecheap than you can use their marketplaces to sell your domains. Hope it will help you.
I think Flippa is a better place to sell both domains & websites, I've sold many websites on there, but only 1 domain sold on Sedo. GD Auction is also a good place if you have account at Godaddy, their price also cheap, about $4,99/year and you can list many domains for sell.
For domain sellers, uniregistry marketplace, flippa, sedo and efty.com are the best ones. Godaddy has a higher commission percentage. Godaddy is best for selling Chinese premium and number domains. You can not sell numerical domains in flippa for good prices. In case of buyers, Godaddy is good one as they have in built escrow service. Flippa is also having a free Flippa Escrow.