Turkey is now under investigation for helping Iran when sanctions were placed on the Islamic republic by the UN, US and EU.
Sanctions prevented Iran from getting paid through the regular banking system or using currency like dollars or euros.
So Turkey paid Iran in Turkish lira, which Iran used to buy gold in the form of gold bars, which Turkey then exported to Iran in what became a multi-billion dollar business.
In return for reducing certain aspects of its nuclear production, some sanctions on Iran are now being eased, including restrictions on gold trading.
Some are calling Turkey's dealings with Iran the biggest corruption scandal in the history of the Turkish Republic.
Al Jazeera's Anita McNaught reports from Istanbul.