To further highlight the sales criteria. Even Russian arms exports are accountable to Russian state control bodies. The Russians have recently sold the S-300 system to Vietnam along with upgraded Flankers. All these deals are accountable and the sales made accountable and public - ie they announce the sales. The same goes for Iran receiving SA-15s and any other arms products. Heavy pressure was brought on Russia by the US not to up the anti and sell S-300s to Iran. This diplomatic pressure was going on during the 1990s.
Russia may not sell S-300 systems to Iran, but may lease them, in my opinion, with the stipulation that they are deployed to protect Russian personnel that are helping to run and build Irans reactors. The day that Iran operationally deploys S-300s will be major breaking news. The US will use it to put pressure on Russia.