I used to have a 21 YO C who only had star potential. I bought him when he was 18 for 20k. When I finished training him, he was 7/7/3/7/6/7 12/12/11/5, IIRC, and he ended up selling for 553k.
(22722238) If he trains the player's secondaries now, at the lowest league level, he will garner more profit on the TL, instead making less because he decided to go with the typical, run-of-the-mill build for a big.