That's kind of how the DDN works in .com/net etc. Many registrars (including Godaddy and Fabulous) agreed on a shared platform that shows domains as available for sale if they're listed on the Domain Distribution Network. Transfers are instantaneous and secure, without Auth Codes, for all DDN-listed domains that sell. The various partners to the sale (the company that first signed up the seller, and the company that drove the lead) share a percentage of the proceeds, generally anything from 20-35% depending on the listing. That's another interesting tweak: you can choose to offer a higher commission in exchange for wider distribution. The higher you go up the scale, the more registrars will pick up the sales feed.
The buyer is protected because once the sale goes through the transfer is instant and irrevokable. And since it's a fixed price system, the first the seller knows of a sale is when they get a "Your domain XYZ has sold" email. After a domain has been listed with DDN, there's nothing a seller can do to prevent a sale (unless they remove the domain from DDN again before said sale takes place)
The seller is protected because the domain ends up at the gaining registrar with standard conditions attached, including the no transfer within 60 days rule. So if anything weird shows up with the buyer's payment during that time, the transaction can simply be reversed and the domain sent back to the original owner at the original registrar.