If they play clean they still lead an unfair game. All year long the media/school keep on putting propaganda for the traditional parties. You might think this is exagerating but just think: How much do they talk about the traditional parties, compared to the non traditional ones? What image is given to them? The state and the rich control the education and the medias thus they want to give a good image of themselves and a bad one to their opponants.
What about the conventions, propaganda ads (also how they use it to influence us subconsciously), flyers...The candidates need cash for all that stuff so they depend on their sponsor(private bussinesses). To get sponsor they make promise to them and those are the only ones they keep because they are themselves involved through investment in stock exchanges and/or owner of companies. Thus they guarentee a financial support and their interests come first.
Further reading:
Disect an ad.Learn how to see the hidden messages in ads. Found in www.pbs.org
How much cash was spent for the electoral campaigns?