The "player monitoring/shortlisting" feature can be expanded so that managers/owners of monitored/scouted players not posted on the transfer list can be made privy of interested managers (i.e., the amount and even names). With that information, the manager of the player garnering attention could (1) begin negotiations for starting/asking transfer price, best listing time, etc.; (2) sell that player once they feel like enough managers have "shortlisted" that player; and/or (3) share skills and flags informing potential buyers. (For interested buyers, when/if option #3 is taken, they can view their intended target in the player monitoring window--again, before the player has been posted on the transfer market.)
For example, I might reveal the skills and flags (with the intention of selling) for my top prospect Scott Nelson if I saw that, say, 10 to 15 or so managers were monitoring him. (I probably wouldn't do so for Nelson but maybe another midfielder. :D)
Alternatively, if a manager is still not interested in selling maybe they could express it using a variant of the current private notes feature--one viewable by the public and accessible by all members, club or not.