Many years ago I had a guy call on a few of my elderly customers claiming to be working for me, even using my name, and he tried to do exactly the same thing. Used the 'could I have a glass of water' routine and then followed them into their property. Fortunately the customers he tried it on were alert enough to know I would never have followed them in unless invited and told him to leave. If memory serve on the third try the elderly lady told him in no uncertain terms to leave and called the police. He had obviously watched me because he only called on my older customers.