If you list a domain name as a fast transfer listing BIN name you need to opt in to sell the domain. Meaning there is a pretty strict check on these. The opt in to sell the name has to come from your registrar where the domain name is registered. So if I had x.com registered at GoDaddy and wanted to sell it on Afternic. I would log in to Afternic and list my name for sale then Afternic would tell GoDaddy I want to sell the name, GoDaddy would contact me and say you want to sell x.com? Click here to authorize this listing on Afternic. I would have to click the email I receive from GoDaddy or whatever registrar I have the name registered with to approve the listing. If I do not then the name cannot be listed for sale. Once the domain name expires, or a lock of some kind is added (such as a registry hold not a typical transfer lock), if the name sells etc if for any reason the domain name can no longer be fulfilled to the buyer then the registrar contacts Afternic and the name is pulled from the inventory list. If the name sells there is a live call to see if the name is available if the name just sold to someone else or just expired etc the call fails and the name is not sold.
Is it possible for a domain to sell when the owner did not list it? Yes but highly unlikely on a fast transfer name, there has to be a really unusual situation and the current owner would have to ok the sale. I am not going to go into the specifics publicly because I know some people may want to use this to try to steal a domain, this would not be possible as we can easily unwind sales with our partners but suffice it to say the situation for this to happen would be extremely rare and hard to duplicate and in all cases the owner needs to ok the listing on a priced fast transfer domain.
Unpriced listings are also checked however there is no registrar level check where the registrar checks as well on these so there is more room for error however these are slow transfers involving manual steps and if there is an error it can be caught during a manual process we have steps in place for that as a back up in case the first ownership checks fail to catch an issue.