Food and trust

Something happened today that got me thinking.  I told a friend I was hungry and wanted soyamilk. He said ok and then after our quiz he showed me a plate wrapped in cellophane. He said it was beans and after a while said it was rice and salad. The nylon looked like it was opened and resealed and I asked why. He said one friend ate from it after a while, he said it was my friend. When I asked her the contents of the plate, she claimed she didn't know. Later on she said rice and salad and she was the one who ate it. Long story short is that I couldn't and didn't eat that food.
I realise that if maybe she was the one that offered the food in the first place, I wouldn't ask so much questions cos I trust her or if it was a sealed package I also wouldn't have asked because the seal to some extent guarantees protection. This then makes me ask.... Whom do you trust with what you eat?
       The suya you buy, the roasted corn and pear, roasted plantain, yam and all that. How sure are you of the safety of that food? Think about it.