It is better to sell players you don't want to keep at the start of the season, then everyone have a lot of money.
And even better, if it is a good player change his name and nationality to someone famous in RL, like Christiano Ronaldo (Portugal)
Then ppl will go crazy and start a bidding war

But if you bought players that will last 4-5 seasons why do you want to sell them now? They are young and they train fast so the star they lose they will get back soon and the value will be even higher, it is older players 26+ that lose value.

But in league 2 you can get players that are 5 QR higher then you could in league 1 so in lower leagues that is a lot so you want to upgrade some players. Sell 2-3 players every season and upgrade the weakest players you got. Most important is a good striker with Free-Kick specialty, a good goalie and try to find a MC that perform high 8+ then it is a keeper.