Depends on the name and the buyer, some examples:
"We have no set price for the domain as it is currently part of our wider development plans. You are welcome to make an offer, but bear in mind it would have to be substantial to justify removing it from our usage."
"Based on past experience, we'd expect this domain to achieve a sales price of $x if we were to market it to potential suitors. If you wish to make a suitable offer we shall consider it"
"We've had several enquiries for this domain of late, and we've concluded that only offers above $x will be put forward for consideration."