To transfer the ownership of your domain, you can do so using the manage profile functions. There's a command to change ownership. You can transfer the domain to another existing profile (you need the user name, password, and name of a domain in the profile), or you can create a new profile to transfer to.

I recommend using a new profile, that way your buyer and you can agree to a neutral profile, and you do not need to grant each other access to your passwords. Given the potential value of domains, you want to keep your passwords very secure.