Iran being an Islamic Republic, its society manifests local customs and standards of behaviour which differ greatly from those of Western world. These Islamic standards are to be followed not only to ensure acceptability in a different environment but also because they are legally enforceable here. Non-observance can result in criminal charges being filed.
Iranians are usually very formal in their approach to transacting business and it will take several meetings or get-togethers before a more personal relationship can be ensured. This is the way to go when it comes to the Iranian government officials, managers of state- controlled companies and foundations. Negotiations will be long, detailed and protracted affairs.
Tenders are mandatory for government contracts related to purchases or execution of projects. However, These are rarely competitive. Dividing the contracts into several sub-contracts is a common practice to try and incorporate local capability and also to negotiate on specific prices. It is recommended to maintain a package approach.

Source
http://www.asiabiznews.net/project-contracts-tenders-rfp-rfq-resources/how-to-do-business-in/Iran.html