I spend around half my life in Iran (for the last eight years).
My favourite example, to show just how pervasive tarof is, was the occassion I was at the supermarket checkout of a large supermarket chain. The young cashier refused, several times, to accept my money. This, at a very western-style large supermarket chain. Of course, I paid. However, a similar thing happened to a Canadian guest I was once travelling with. At a mini-mart, he tried to purchase a bottle of water but the guy at the counter refused his money. The Canadian took the offer at face value, and left.
A few minutes later, a very sheepish guy come down the street asking the Canadian if he wouldn't mind paying. Iranians will understand just how only-in-Iran this situation is.
One thing basically every foreigner who has visited Iran will agree on - tarof or not, Iranians are the warmest, most welcoming people on the planet. The truth is that an Iranian will never understand just how much fun it is being a foreigner in Iran, we really are treated well (tarof or not).