Under the Iranian system, you cannot run for office without the approval of the guardian council. Therefore, the Guardian Council effectively has control of the government. They can prevent anyone who does not share their views from running for office.
http://news.bbc.co.uk/2/shared/spl/h...ml/default.stm
See the red dotted line? That indicates that the Guardian Council has a veto on any candidate running for office in Iran. The Guardian Council can arbitrarily deny you the right to run for office.
That one red dotted line is what makes Iran a non-democracy. Thats it.