I've got a promising young player to sell you, he's played a part-season in the PL for the worst team in the history of the PL. Despite looking good in parts he's struggled for consistency and in fact he's only scored two goals.
I'd like to sell you one of the standout players in the Championship, he looks stronger and fitter than last season, has scored a dozen goals and has seventeen assists, and is a regular in the England u21 side.
Option A we get money to buy (several) players for a promotion side but lose one of our genuinely PL standard players.
Option B , we get a season of him in the Championship, if/when we go up we cash in (and swap our crown jewel for the 2020's version of Speedie and Dixon).
B for me, but it's not my money.