How do we know if the peaty/smoky flavor of the whisky comes from liquid smoke?

I am sure this has been asked before, but I couldn't find it in the forums. In this day and age, there are methods of faking possibly anything. When we buy an Islay scotch, how can we be sure that the smoky flavor we get from the whisky is not achieved by putting liquid smoke in it? How do we know for sure that it is from the peat used during the kilning process?