Lonely Planet site has this to say: "a Farsi word that is at the heart of Persian culture. According to Lonely Planet’s Iran guidebook, ta’arof describes a system of formalised politeness that can seem very confusing to outsiders, but is a mode of social interaction in which everyone knows their place and their role. In ta’arof, two people will try to show their deference to the other by repeatedly offering food, hospitality or anything at their disposal. For travellers to Iran the most important thing to note is that taxi drivers will often tell you that the ride was free, or offer it to you at a lower price. Not true, this is classic ta’arof; travellers should pay the right amount to avoid annoying the driver. That said, sometimes an offer will be genuine. Knock it back a couple of times and, if it’s still being offered, take advantage of Iranian hospitality."