They likely arrived in a foul mood and you just happened to be in the line of fire. If they are still foul tomorrow, then they are just foul people. No way to win with them..
It does happen. Last week I had a lady staying for 4 nights. On seeing the room she insisted she'd booked a double not a twin (which she hadn't because I can tell from my booking system log and copies of confirmation emails). She then moaned about the view not being what she expected. I was fuming and ready to show her the door.
When she checked out she said we have a beautiful property and she was sorry she was grumpy when she arrived.
I've also had people who seemed grumpy and miserable throughout their say, who have then written wondrful comments in the visitors book.
I do tend to steer clear of people like this though, they don't get the same attention as "nicer" people, their loss.
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