[Fyrzowt]

"I'm sorry, I only give tours when I'm camping."

I suppose each situation is different.
You don't have to be paranoid to be cautious and safe. A healthy respect for your instincts is warranted. The ability of the subconscious mind to recognize trouble is well documented - ALWAYS trust it until you can prove that you picked up false cues.
Each situation is different: Daylight/nighttime or reduced lighting? Location - other folks around? What is your ability to react to a situation that would put you in peril?
Treat this type of person as you would a door to door sales person. Do you normally let them in your house? I don't for a variety of reasons, safety for myself and my family is one of them.
Dave