It's especially true if you play on hard or higher. They will just make more money if you pimp them yourself at night.Did you play on hard?
I assume that shady guy is that guy with escort requests - totally not worth it since you can't use girl for 3 or 7 days. Just do it for achievement with some reserve girl trained to barely met requirement.
Selling girls is the same thing - totally not worth putting time to train them just to sell them since they will make you way more money at night. (examaple: fully trained Werewolf (9 in all stats except affection and many useful taits) sells for 195k with base price of 3k, while she can easily make over 1 mil in one night)
Auto training is slow and it's expensive to get it, plus you can't use girl for 3 days minimum. So it's also not priority or even decently useful.