My daughter has a friend who I have seen grown from a large to obese over several years. Recently she stopped in to visit. She and my daughter sat at the dining room table chatting for a while and then left. Later I noticed that the chair that my daughters friend had sat on looked strange. On examination I discovered that the wooden bottom of the chair which is hidden behind fabric was broken. I've since had the chair repaired. How can I politely prevent this from happening again.