No, I do not think that Donald Trump is correct in calling Hillary Clinton a "world class liar" because Donald Trump has also been caught lying and this seems very hypocritical. Donald Trump's presidential run has been full of different scandals and controversies and he certainly doesn't seem to me like a morally sound individual.
There really should be limits as to what you will do as a candidate. We have never seen a candidate like this before. He is aspiring for the highest office in the land but has absolutely no filter or class. As rich as he is, he lacks decorum. Calling a woman out of her name is the lowest form of manhood.
Donald Trump is the king of liars himself. He often changes his position and denies saying things he actually said. Even when confronted with video evidence of his statements, Trump lies and says it wasn't him. Every politician, including Clinton, has problems. However, Trump is the only one with the level of cognitive dissonance to see past footage of his own contradictory views and lie about it.
Hillary Clinton has had credibility and trustworthy issues with many in the electorate. Clinton is often viewed as being dishonest. However, Donald Trump should not have referred to her as a "world class liar." Trump should select his words more carefully when taking on Clinton's trustworthy issues. Instead, he could simply bring up instances of where she did not tell the truth. This would sound more serious than simply calling her names.