I wouldn't say it's good management, but I also wouldn't call it a problem :P
Buying and selling players is a perfectly good strategy, I imagine you can end up making a lot of money by finding bargains on the market and then selling them. But long term won't this catch up on you? Because with the higher amount of taxes you'll have to pay I would guess you'd reach a point where it's tougher and tougher to strike good deals.
I don't think it's a good move to sell trainees, but someone may disagree. Essentially it's cheaper to train than buy talent. Even if you do find vets on the TL that can get you promoted, how good are your chances at the next level? Working on trainees you have some control that ensures that your team keeps improving, and you can always sell extra trainees to upgrade the positions you're not training.