Depending on the auction house, domain name registrar, and type of auction, a domain name may be locked for a period of time following the conclusion of an auction. This means a domain name cannot be transferred out of a registrar, and it may in fact be locked within the account and unable to be pushed to another account (again, this may depend on the registrar).
Because I sometimes receive an inquiry during the auction lock period, I want to share a bit of advice with how I deal with this type of situation. Before responding to the inquiry, I will do a bit more research on the history of the domain name.
If the auction was a private auction and not an expiry auction, I might contact the auction house and registrar and ask them to remove the lock for me. If the domain name has been at the registrar for more than 60 days (and is older than 60 days old), the auction house might remove the lock for me. This is especially true if I have been a long time bidder and there is very little risk of me placing a credit card chargeback or something else that could cause them to lose money. The registrar might not be willing to unlock it, but that is the first place to start.
If the auction was an expiry auction or pending delete auction, the chances of having the name unlocked are very slim. Again, this depends on the registrar because some registrars allow outbound transfers following a expiry auction and some do not.
Knowing whether or not I can have the lock removed is important. If I can transfer the domain name out, I likely won’t even mention anything to the prospective buyer. If the domain name can be pushed to a different account at the registrar but not transferred out, I would likely mention the fact that I just won the domain name in an auction during the course of my negotiation. This way, I can reference the auction and the lock status if we are able to come to terms on pricing. Finally, if the domain name can not be pushed or transferred, I might either not negotiate with the prospect or be totally transparent up front.
I think it is important to be up front with the prospect as soon as it is feasible. I would be annoyed if I spent a few days negotiating to buy a domain name only to find out that a deal can’t be closed for days or weeks due to a locked status. I also believe mentioning the auction can be helpful because it likely shows that the domain name was in demand. The downside is that the prospect may be able to find out the sale price and use that in the negotiation.