If everything is legit, it can't be a scam even if he charges your friend $500. He quote the price, you pay the price. So it's your friend's choice whether should he choose to do or not.
But whether the pickups are brand new or it might not be a dimarzio, then it's a different story. Of course if the receipt stating that it is a dimarzio being installed and in fact it's actually another pickup, i believe you have the right to sue them.