Don't worry...I'll know. But it is a fair question.
In general, I will know by their overall understanding the REASON why tyranny is created in the first place, MOST of it from "good intentions." Such good intentions include "getting along" with the democrats, which today is tantamount to getting along with Stalin, Castro, and other dictators.
If they've not just read the book, but can recognize the progression of tyranny that is now so blatant with the current congress, media, and Europe, then I consider it a success. I cannot imagine a true conservative who, after reading the book, can honestly legislate against its tenets.