>just asking that one question would be enough to screen out most fake service dogs
This seems to be true. About a week ago I witnessed my boss question someone on if their dog was a service animal. He was adamant that it was but his demeanor betrayed himself.
I never saw someone get so maliciously defensive before, the person had to be told to leave because of his attitude from that point on. He actually called back and threatened my boss (on voicemail!) some time after leaving.
That one simple question blew him out of the water. Dog seemed nice despite his owner, but it didn't seem to be doing anything but dogging about.