Scam in seeing homes

I would like everyone to be aware that in Schaumburg there was a man that knocked on a door of a home for sale and said he wanted to see it.  The home owner told the man to call the Realtor on the sign or their own Realtor.  The man was insistent that he was very interested and would really like to see it.  They did not let him in.  Another home in Schaumburg did let him in and was robbed.  Please be aware that if you are selling your home, town home, condo, duplex in any area including Schaumburg, Streamwood, Roselle, Bloomingdale, Bartlett and any other please be cautious and only allow your home to be shown by a Realtor who will give you identification when they enter the property.  Susan