A Valuable Lesson for my son

Today my son learn a valuable lesson and he is only 5 years old ; Never to touch anything that has been opened. The store owner bring this suck bottle sweet to us to tell us he has opened it to suck. I asked him and he said he didn't open it nor suck it and I believe him. Then I ask him if he touch it and he replied yes. Thus, we paid for the sweet and threw it away. Why? He did touch it and who are we to argue that he didn't open it? So we told him this lesson, next time see things like this, DON'T TOUCH IT!