If they rang your doorbell and announced they'd come to stay for a few days.
Relative and I are in disagreement! Relative thinks it's a nice surprise and if the visitor doesn't mind what state the house is in and/or whether you need to leave them to go to work, then it's all fine. You should be happy to see them and grateful they made the effort. I think it's massively inconvenient and would far rather know the person is coming so I can prepare, maybe book a couple of days off etc.
We're struggling to see each others view point on this so I'm curious as to what other people think.