Don't worry on it, as nobody ever wants to sell in negotiations. I think I have managed to buy ONE player through it, after dozens, and dozens of bids.

The fact is, the players that are on there, are not chosen by the managers, they're simply put on the list because they're nearing level up. Meaning, they're usually the very players managers want to keep!! Unless you make near scout level offers, your offers will mostly be rejected.