it`s better to sell player`s that end with 4 or 9 for example your keeper is 81 if was 79 then level below will sign as top end of 5 star ( that`s if he`s 5 star at 81 ) it also depends on age the older the harder too sell, also most player`s have made signing`s but train and sell last couple of season as those that don`t get promoted will try and player`s for as few tokens as possible for season or sell on first two of new season and hope for bidding war