I'm with seelenjaeger. I don't agree with the idea that training should generate a huge net profit when considering the final sale price versus trainee purchase/trainer salary. As it stands, I'd guess a well trained player gets you something close to a break even point, maybe some profit with an intelligent build, less for a primary skill pump build.
But there are still huge benefits to training, that being the savings on player salary versus effective player skills during the season that training occurs. At that point your team is getting a discount in terms of the player's performance, and you team is playing better for cheaper. That discount can get very big when you're talking about high skill trainees, as the salary increase from marginal primary skill pop gets very, very costly.