Many times if they want an extended chat they will even take the person out for coffee, just to get a feel of the situation and ask questions.
http://www.banterant.com/2013/08/homes-for-hackers-gets-visi...
Yes, if an investigation is more serious then the FBI can be very intimidating, such as: http://arstechnica.com/tech-policy/2014/04/whitehat-hacker-g...
I'm just saying that if the FBI did investigate me there is a reasonable chance they would act civil and objectively rather than abusing their power and using unnecessary force, and that's the way it should be.
You see, having to explain what you do and why you do it is already a limitation of your freedom, and has chilling effects on society as a whole. If there is no indication I have done anything illegal, it's none of their business, I don't have to explain how I live my life and why, to anybody.
Disappointing lack of common sense from these commenters.
The prior probability that someone has bugged your house isn't affected by their claiming to be an FBI agent and taking you out for coffee. That's because, if you secretly bug someone's house, it's a secret. They would be doing it either way. (Or not doing it, because what are you supposed to find exactly?)
It's part of their job to sanely estimate the credibility of reports. If I can phone the FBI and say something that causes them to send an agent to track someone down (or worse, to sent a SWAT team), there's a serious problem with the way they are performing their job.