For company name it could be name of recruiting company (not actual employer) or just plain fake.
Besides, sometimes employers don't want to advertise their openings publicly (may be to avoid getting flooded by irrelevant applications or prevent panic among existing employees).
There would be a sort of self-selection that would come in to play - the only companies that would advertise there would be companies that are comfortable being public with that sort of specific information.
The salary one would probably need to be a range - $60k-$75k, for example. This sets expectations on both sides, although it might not stop a lot of misfit submissions, but those aren't generally stopped now anyway.
I'd have a "flag for false data" link.
Also, if you did this in Australia, then you could have an ABN number field that is mandatory to be filled in.