I've noticed that some rare items (Big Nugget, Pearl Strip) has a unique description that says only a maniac would buy it from you. Trying to sell these items at regular pokecenters doesn't work. Does anyone know where you're allegedly supposed to sell these items?

I know there's a Baker on Route 5 in the RV who will buy rare food items for a large price.
There is a person in Iccirus City I believe who is a maniac for gold nuggets and pearls
Lastly, there is the maniac in Undella Town for artifacts.

(Not sure if I'm forgetting anyone. Someone feel free to comment if I left anything out)

Time to teach about item maniacs~!

Food Maniac- Located on Route 5, this maniac will purchase any delicacy for double the price of what you'd get at Pokécenter Marts.

Ore Maniac- This dude just wants an ore that'll shake his core! He's found in the Icirrus City Pokécenter, any stones that you find can be brought to him and sold for high prices.

Relic Maniac- This maniac is located in the Riches house in Undella Town. He'll buy the items that you find by using Dive in Undella Bay and also the pathetically useless Flutes.

Mulch Maniac- Got mulch from a Grotto? This maniac on the Mistralton Airstrip will buy it for quite a bit.

Rare Bone Collector- On Route 18, there's a dude who collects Rare Bones. That's all I know, I haven't been there yet.

There's a berry one as well, or is that the food maniac?