Get ready for an IRS audit. better not to answer the door
Excellent advice. There is no law or requirement for me to acknowledge a knocker's existence.
The same is true with text messages and email and phone calls from random strangers. Silence.
The risk in answering the door is that you surrender your position. If it's a stranger, they're asking for money etc. if you decline, they can vandalize/egg your homes etc. If you accept, you're on a sucker list and more will come.