Just some observations here to share.
Each season I always sold some 9-10 players and always set sold price as max. It used to be within minutes to up to 12 hours, and sold value typically was 1% less, 10%-50% more to up to a double of value if gets really lucky (only had that once though).
Last season I did the same max sold price for the 9 players. All 9 got sold within 2 hours (most sold earlier before matches, and a few sold after last match) though every single one of them would only be 95% of the stated value.
Maybe there’s luck that mine all got sold soon, but it seems that value gained would not be as much as before (there was a time in the earlier level 2-4 that I would not hesitate in buying a lower quality 1T 18/19yo as reserves, then manage to get a better sub, and then train them to exhaustion for both the manager training experience and small increase in quality, then auction them in hoping for a significant gain in value when sold). Lower level managers would find it more difficult to gain sufficient flowing capital for ground expansion because of this, and probably slightly hindered in bidding for FTs with less money saved from player sale.
Just don’t fall for the trap in buying scouts for temporary solutions, as that will further slower the value gained by 1 less training player.
Assistant manager recommended player, with which the sponsor paying the full price, is a very good option as that will save you a lot of money stuck into a top FT who you would always keep and can’t gain value from (that player would stay for so long in the team that he is not worth much when we actually sell him).