Is life so simple?

It's been a nagging question that's been on my mind for several days. I can't get it out of my head. And the question is this:

In the context of today's society, if someone makes a very serious public accusation against you about an alleged offence and later you deny the allegation, should the denial be accepted as a gospel truth without further questions and should it automatically absolve you of the alleged guilt?

I've been unable to get a satisfactory answer to this. Can anyone help me? Please??