@Mike-And-Jane0 Actually I've just gone and had another look, comparing my calendar to what the 'preview' is (what I presume is how guests see it) and it seems it is variable as to how my blocked dates are showing up - sometimes they are a grey (available dates are black), and sometimes they are crossed out light grey (like the booked nights show). So I'm not sure why the difference, and I can understand the confusion on my guests' behalf.
I would have hoped that all my booked and blocked dates would look the same to the guests.