Hi @Mike2542
In my area we tend to use duvet covers - these are absolutely washed at every change-over, along with all the other linens.
Interestingly, I noticed that in parts of the US there is a tendency to use "comforters" which have a warm inner, but the cover is not removable (??). I don't see how one could possibly not wash these after each guest, but I find it strange that one would sign up to wash (and dry!) such a huge bulky thing so frequently. So personally I'm still confused about how comforters with non-removable covers work in an Airbnb (perhaps someone can explain), but that's not really your question! Yes, wash it all every time.