Driving around Tehran, you'll see Rafsanjani 'supporters' are everywhere. But things are not how they look like.
Many of these young boys and girls on the streets are not going to vote Rafsanjani. He is just an excuse for them to gather and have fun. The same way they gather during religious Shia festivals for Imam Hossein. They look like they are genuinely interested in what they do, but if you start talking to them, you'd see they are probably checking out hot girls and boys behind you.
Along the same lines, polls are usually not reliable when it comes to Rafsanjani. Best example was sixth parliamentary elections in which he was at worst among the top five, but ended up in 30th place.
I believe one third of survey respondents lie about who they are going to vote for. Rafsanjani's name is enough to scare many ordinary Iranians. They think they'd be in trouble if their answers were not what they guessed the interviewee wanted. They are amazing actors in this game.