Hmm, seems to be a question of luck. When we went through this summer, everyone was really nice and helpful on either side. Someone made sure our carnets got to the right counter and did not want any money for this. No x-ray, no search or such, just checking frame and engine numbers. There also was a smartly dressed chubby guy asking for our documents, but we did not play the game and he was alright with that. Then there was another one, quite vicious, trying to scam us into buying a 'mandatory insurance', scaring us with stories about how illegal it was to ride without it. We asked for the price and politely told him we were not interested and he got angry trying to get some baksheesh for letting us off, but we told him to go and enjoy his solitude somewhere else, which he did. Never pay people to leave you alone - your just showing bystanders how to make quick money.

Iranians are extremely friendly and nice and you hardly find someone who is not - but if you ever get into a bad situation, just don't let anyone intimidate you. Physical violence has pretty high penalties on it, so even if people get agitated and seem on the verge of snapping, they very unlikely ever will. Just keep calm, state your points repeatedly and walk away if you can or get someone local to help you.
For every crook there are five bystanders who will come to your help.

I had a pretty nasty fight with a taxi driver in Tehran who tried to scam me into more fees. Took fifteen minutes, I walked him to the desk of my hotel and told him to call the police and in the end got my money back with him dropping my luggage on the pavement and shouting and swearing at me.

Just keep calm.