We do not currently have a built-in feature to “hold” a listing for a specific buyer. However, if you have communicated with a buyer and a purchase price has been agree upon, you can manually adjust the listing title to indicate it is reserved.
For example:
Edit the title to say “RESERVED FOR [buyer name]” or “HELD FOR [buyer name]”.
This signals to other buyers that the item is set aside for someone else, though it does not prevent others from purchasing it.