Man, I must tell I really enjoyed you guys writing about the economy and prices in the alchemy shop, to answer you some questions:
The reason why our hero can't just make Dianna give him everything for free is simple - As you may know, she is a magician so charming her is much harder than the regular person (A reason why MC had to use a lust potion), and even when she is under a charm that's doesn't mean she can't break free so using her too much can possibly make her realize that's something is no yes lol. At least this is a more "story/plot" reason and for gameplay reasons, it would be too easy ᕙ(⇀‸↼‶)ᕗ.
But I have some plans like after you progress her story and take better control over her you can take over her shop or something still thinking about it. (If you have any idea feel free to write it.). Also, I think that maybe making some of your adventures friends go look for herbs for you can be a good idea, but same still thinking about it.
Anyway, I agree that making potions is less profitable than it should be, so I probably make some changes in the next ver. like buying ingredients and making potions will make you a small profit but looking for them yourself will give you much better.
And I am really sorry for the bug in the camp, It's a small error and you can just ignore it, but still, it's my mistake and I am sorry for the inconvenience.