I had a similar survey/interview last Summer, from a representative of one of the prominent marketing companies. The guy was legit as I checked him out before the survey was conducted. He held no data on me but was somewhat pushy for me to give him as much info as possible.
I thought it strange at first as he knocked on the hall door.
He came into the house set down and the interview lasted approx 45 mins. Quite intrusive questions may I add. How much was owed on the house, was I in NE, which bank issued the loan etc. All I got was a pen and some fancy paper for my time!!!
Joking aside I found the experience rather strange.