DEAR MISS MANNERS: My sister-in-law started keeping her dining table “set” about 20 years ago, when her home was on the market. I gather this was a staging thing. She still does it. It just seems unclean to me. Is this one more of the many things people do that I’m in the dark about, or is it weird? GENTLE READER: Definitely weird. It evokes images of a dinner party where the guests never arrived. Not to mention, as you have, that the settings must be getting dusty. It is your SIL’s house, of course, but if you feel so compelled, Miss Manners suggests asking, “Are you expecting company?” — wi…