I've done quite a great profit selling players after 1 season with lvl 5 and lvl 6 coach, you can check my transfer history and take a look at Alaric Savary, 18 french players, who came in at 56 TSP and left out at 75 TSP, how much profit did I made in 1 season just with him? 1 Million!
Wow man, that's hella amazing. What did you do with him xD that is an amazing success story. How was his skills when you sold him, and I assume he would have been 19 when he was sold? Other than a superior trainer, did you have any youth trainers as well?
But I do agree with you that getting 6 trainees and going 1v1 for the whole season would be more profitable.
There are still plenty of people who train Cs (especially in my country, probably because we keep getting tall MVP/HOF draftees). But I assume people who flip players for money would rarely choose to train Cs, particularly because there is no training that pops as many skills as 1v1 forwards, and handling is height dependent. Hence it's not that easy to get a lot of pops in a short time.
Also your guard search, what skills did he have prominent or proficient in? Because for a guard only OD and PASSING add him real value, Driving / Passing / Jumpshot barely add any value to his market value, in my experience
Iirc it was 9 JS, 10 HA/DR/OD and 8 IS. But it's midseason, so it's understandable that he isn't going off for 350k, coz he'd be 20 in a few weeks time.