Well when you park your godaddy domain on sedo you point the Name Server to sedo';s nameserver for the parking page & traffic stats. This also helps when you post this on the marketplace where it shows up the "Hits to this domain name" according to the number of hits this parking page gets when the NS is pointed to it. When you have a successful transaction you can transfer the domain name to the buyer's godaddy for free. I am sure every domainer will have a godaddy. If in case the buyer doesnt have a godady you will have to transfer it out which will cost something.