The enemies you fight in raids may drop some items you won't find a use for. The residents of City 17 are very interested in these items!
Increasing your reputations with the various residents will reward you with extra bonuses such as increased sale prices and additional end raid loot.
You can increase the reputation you have with them by giving them gifts (It states it on the item who it is meant for) or emoting.

Eli / Auctions:
Reduces auction tax by 3% per level
Kleiner / Raid End Loot:
Increases raid end loot by 2 per level
Nick / Shop:
Increases sale return by 2% per level
Mike / Shop:
Increases sale return by 2.1% per level
Cheaple / Perks Shop:
Decreases price by 2% per level
Tyrone / Black Market:
Decreases price by 1% per level
Odessa / Farming:
Unlocks better farm plots 
(Better soil = better rarities!)
Increases fish size per level