At your level try to sell at the end of season. The only players you can keep to sell at the beggining of season Will be those with special ability or triple role, but even those it is dificult to have bid wars on level 1.

Selling them now you get 90% of there value, maximum price you can ask, at the beggining of next season there value Will be around 70 or 80% and to get the same amount you have to expect a bid war. Not very likely on level 1 or 2