The tip...

“	Do not sell all items in one bulk, as they will count for only one training. Sell them in separate amounts, but make sure the profit earned satisfies the requirements.	„

Wouldn't you risk under profiting at that town you're in that selling the highest due to that?

If you miscalculate, yes.

Just divide the training amount by the profit gain of the item, and that tells you how much items you need to give. I'm not sure where it rounds to, but I always round up.

For example:

• 5,000 / 300 = 16.667.
  • (Training Requirement) / (Profit Gain) = Selling Item Amount.