This is Dr. David
it is always possible a patient could have gotten sick after eating your chocolate.
but if they didn't wash their hands before eating, it could have been virus or bacteria on their hands which caused them to be sick.
or it could have been food that they ate before or even a day before which caused them to have diarrhea or nausea.
there are always people out there trying to get something for nothing.
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it sounds like it would be very very unlikely that your chocolate was what make the client ill.
but there are people out there who are allergic to peanuts who don't know it or allergic to glutten wheat protein
and these ingredients could have been in your chocolates as well.