Have a look into the way modern day scams are carried out. They are ruthless and are able to get to a large number of victims.
The scam itself (Firewall at 2% etc) should be pretty easy to spot but they get around this by targeting people who are less likely to have knowledge about such things.
The whole operation is run like a legit call centre business (except that it's a scam) with full-time employees on a monthly wage who are taught what to say & do at every turn.