Ugh, those clues are painful :( Ok here we go though.
Remiel: Radiation or Powdered Drug // Confidential letter, possibly Antique if there wasn't a location card that fit that
mia h: clear because I see nothing poisoning on hers
MP: Poisonous Gas, Wine, // Again maybe button? But I don't think I would have picked bookstore for that. Maybe there wasn't any other store, but some room in the house might have worked better?
Yugi: Clear, same reason
Rapt: Venomous Snake, but nothing really for bookstore. Unless he was thinking you buy the water there, like college bookstores usually have a bunch of drinks too. But it's a stretch.
Christa: Alcohol // Note (Switch? What is this? Lightswitch?)
Mintprincess: Chemicals, Mercury // Banknote (weird translation, it's cash), Dictionary (As pointed out)
pheonixrisen: Dirty Water // Magazine, maybe Numbers?