Too often society paints with a broad brush. Yes, there are lying, cheating and self-dealing politicians. However, there are liars, cheaters and self-dealers in every profession. Humans are not perfect. Is it possible that more politicians are liars than the general public? Yes; however, it is just as likely that the percentage of politicians that are liars is similar to the percentage of liars that exist in other professions.
I actually believe that there are many honest politicians, but sometimes it's hard to find them. All too often we hear the stories of lies, deception, and corruption and rush to assume that all politicians are the same. Trust me, if you look hard enough, you will find many politicians that have been honest throughout their careers.
A truly honest person could never become a high ranking politician. Making friends in high places is what makes or breaks you, and sadly this will always involve money in one way or another. Politicians are greedy by nature, so while they may have the best interest of their people at heart, it will always come second to the power and money.
Power corrupts and absolute power corrupts absolutely, a wise man once said. Every politician says that they are going to end corruption. And every politician ends up being corrupt and just as money hungry as the next one. There is no stopping it, other than to limit government to very limited powers.