Have you ever had someone take you up on an offer, when you really didn't expect them too as you were being insincere with the offer originally?
e.g You have said "Oh, you must come and stay with us, when your next in town" and you get a phone call a week later from said person asking to stay with you.
This has happened to me a couple of times. Once went swimmingly; the other time our friend brought 2 people we didn't know along with her, and I flatly refused. We have never heard from her since