I forget how long ago exactly but at one point the Hugel fruit shop was changed from your regular NPC shop with items that could be bought at discount prices on merchant characters to this.
We have multiple items that increase the effectiveness of slim potions from both the kafra shop and naturally occurring in game (See list of those items below). It would also provide a more appealing and much needed (albeit small) Zeny sink as well as a more affordable source of high end healing items for newer players.
Telling Doll (Rather old and probably not readily available anymore)