Yeah, quests shouldn't reset the same day. You can force a reset be exiting the game and loading it again, but otherwise you get 5 quests per day per trader and that's all (not counting special quests like that dig quest or open trade route quests). As a side note, there is a bug that's been around since at least A21 where you can end up seeing another player's quests in MP and even select those, making it appear that they reset and allowing more quests to be taken in a day.
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Yeah, quests shouldn't reset the same day. You can force a reset be exiting the game and loading it again, but otherwise you get 5 quests per day per trader and that's all (not counting special quests like that dig quest or open trade route quests).