I don't mean to disparage all businessmen, but Trump has made his money by lying and hiding the truth. There are several reports of him not paying his contractors and then declaring bankruptcy when forced by the courts to pay up. I think he just accepts that he is allowed to hide the truth and he's been getting away with it for a long time.
Yes, Trump is a liar. He lies about everything, including his health and his views on Obama. Earlier today he claimed Clinton started the birther movement, which has been proven to be a lie by every major news network. He thinks he deserves the best so he will lie to get there.
Yes, Donald Trump has consistently proven he is a congenital liar. Just today, he made this "huge" announcement about his stance on the Obama birther situation. He has said that Hillary Clinton started and perpetuated the birther rumor, which is untrue. He has said he was going to release his taxes, he still hasn't. He said he was going to release his medical records, he released some weirdly worded letter from a doctor who is now not so sure how that letter came to be. And that's only happened in the past few months.
To be fair, I do not suggest he is not a liar but I do not think it politically correct to call him a "congenital" liar. The definition of a congenital liar is someone who just can not tell the truth. Trump probably can tell the truth in many situations. He just chooses not to, is told not to, or is found in a situation where the truth is skewed. All politician or anyone in the political field are in this situation. They rarely tell the truth, especially if it will not benefit them, but they are choosing to do so.