Can a seller, who has listed an item for sale, change his mind and decide not to sell the item?
What are the seller's obligations to a potential buyer after speaking about a sale, but no formal offer or agreement had been made?
The Gemara considers it praiseworthy to make good on one's mental commitments, as Rav Safra did. However that's not required by the letter of the law.
If someone said "I will sell" but took no action on it, then we conclude "it is appropriate to follow through, and failing to do so disappoints our Sages." (But the counterparty has no legal recourse.)