I've met folks like that on a few of my Park Ranger or other interpretive tours over the years. After a while you realize that if you don't take control they're going to lead your tour by proxy. I had an old guy do that to me at Ellis Island one time when I was just starting out. After that, if I had an interrupter or an arguer, I would pause and explain to the whole group "sir, this is my tour. Your opinions are in conflict with the research I've conducted. Please wait until after the tour and I'll happily answer your questions, but for now, let me finish my tour." When I was in places where I was working for tips (private sites) this often times resulted in larger tips. :)

SRS