Top 5 Hearts?
A:
You can see which heart vendors you need to have unlocked by clicking the red arrows next to the top five ingredients at the beginning of the ‘Top 5 Hearts’ guide. It gives the name of each karma vendor and the map, you can cross check the wiki for an exact location and then see if you have it completed on your map already.
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I’m not much of a crafter, but I’m assuming they’re referring to the ability to use karma to buy ingredients from heart vendors after you finish the heart quest in an area. Different vendors sell different things, and I’m pretty sure some ingredients are either exclusive to one NPC or are only available from 2 or 3 NPCs. So “no hearts” refers to just stuff you can get by exploring and regular vendors, “top 5 hearts” means you have access to the 5 NPC vendors who ingredients are some of the most cost-effective for leveling cooking, and “all hearts” presumes access to every ingredient in the game.