Hi! Thank you for playing!
After you give them a price, the students will always try to go to a lower price from what you say, so you need to try to sell the candy at a higher price for higher profit (if it is too high then they might flat-out refuse).
Also, after they say their price the bargain starts, and you can convince them to offer more by pressing E repeatedly. You’ll see a bar filling up, and the price increasing every time it reaches the top. If they don’t refuse your price, you can always get them to match your offer.
As for the price setting, thank you for the suggestions. I really like the [+1]/[+5] idea. I’ll try to improve it for the next update, along with other ideas and features I have in mind.
:)