I can pretty much debunk 1 and 3 personally. Good companies and people take hiring very seriously.
E.g. woman buys new shoes on pure impulse. At home she finds they go really well with a certain purple dress. Why that's precisely why she got them, of course. Eight months later, that's all she remembers: I had that dress in mind when I saw those shoes.
(There's at least one study on people with severed brain stems that is fascinating in this respect, but I can't remember where I read about it, and don't have time to track it down)
I know that very few employers would take the risk to be so frank but I personally wish they were. It would be helpful to the candidates who actually care about improving their knowledge and skills while potentially offending those who are trying to fake it.
I've told candidates variants on that theme before.
"This position requires knowledge of programming, particularly in (C, Python, insert details here)."
Dancing around that point is not a "politeness".
That was, incidentally, sekasi's point #3, several parent references up:
"3. Always respond to requests for more information"
"3. Within reason, always respond to requests for more information."
Many communication "rules" require the ability to moderate one's interpretation of the rule. I don't think this is any different. It's a good thing to give candidates feedback and if they're confused, the feedback did no good so you should be willing to help them understand. But if they're just unwilling to see the world or themselves for what they are, it's out of your hands and you should leave it well enough alone.
Following up on some references before calling people in for an interview isn't a bad idea.
Man, I have seen some blatantly incompetent ones. You'd give them a white board and ask them to show a linked list with boxes and arrows. They just couldn't do it.
One case I remember couldn't demonstrate pseudo code for a circular buffer operation based on an array with a head and tail index.
Hash tables might be a better filter, because IMHO you're a lot more likely to find those in real use these days than linked lists.
(The job area was embedded development, involving C and C++, so asking for C code related to linked lists would have been fair game!)
And (hopefully) how well they did in the phone screen...?
(These werr people who couldn't program FizzBuzz)
Plus anyone can just make shit up on their resume.