I just remember MIL and FIL saying that back in the day C'Link used to send people around to check up on 'house mates' of the opposite sex to make sure there were indeed separate beds and clothes were stored separately etc lol... not sure if it's true or if that would be legal in this day and age but I certainly haven't ever had anybody ask questions of me that I hadn't opened myself up for (by walking into C'Link and making a claim or contacting them personally to change/update details etc)
Fraud investigation still do that at times, although its usually not necessary - most people are caught out through data matching with banks, super annuation funds, insurance policies etc...I have a friend that recently transferred to the fraud investigation squad and has been told that she may be required to partake in unannounced inspections of people's homes.