Yes.
no
Yes, it is illegal to pretend to be a doctor or practice medicine without a valid medical license. Doing so can result in criminal charges and serious consequences.
yes
No, it is not illegal to put up missing posters in public spaces.
Yes, it is unlawful to have a vehicle with a missing VIN plate.
I believe that it is illegal to pretend to be someone else that actually exists. However, if you are pretending to be no specific person, and just lying about your description, it's perfectly fine. It is also illegal to pretend to be a Doctor, or any other authority figure. By the way, as long as you are not DIRECTLY disguising yourself as someone (I.E your best friend), it's legal.
no i dont think so. why would it be?
If you are trying to defame and/or defraud someone of goods or services, yes.
Yes, it is a Federal Crime to mis-represent one's self and can be prosecuted as fraud.
It isn't illegal unless you are pretending to be homeless to either harrass someone or for illegal purposes. eg. Nobody would expect a homeless to be carrying a secret supply of and illegal drug...
Yes, but you must tell the potential buyer that it is missing. That it may be illegal to drive the vehicle without it.
A legal drug that works as well as the illegal ones?