Can they do this? (Score 1)

Let's say I buy a bag of assorted candies for $5 from a grocery store. Someone then comes up to me and claims there is a piece in my bag that belongs to him, which someone has stolen from him and put it in there deliberately. I ask him politely to tell me which one it is so I can give it back to him, but he refuses to let me know and instead says I owe him $100. He says if I don't pay him he will put me in jail.

Now please tell me, how can something like this be allowed to happen in any civilized society?