I've been cancelled on twice now after I've been given the postcode. It's all down to comms. Polite cancellation is way way better than complete radio silence and then being stood up too.
I'd much rather a WG cancelled on me if they were ill with a cold or something, than soldiering through with a sub par booking, in which I might catch what they've got. Hopefully much like any good WG would prefer us punters do.
I really want as much notice of a cancellation as possible, definitely before I start travelling. It's all down to how well they deal with it and their comms. I got an honest phone call once from and a sincere message another time. I rebooked one, but the phone call arrived while I was en route, and I just wanted to punt whatever with an hour to go, so I booked someone else (who was a lot cheaper and really good). Unfortunately I never got motivated enough to go back.
After a cancellation, if I later see a field report later for a different booking the same day then I'd leave negative feedback and a poor review.
If I'm ill mysef, then I'm out for a long time while I recover. I don't know what happens with other people but it's weird how cancellations never happen with more than a day's notice. But people are arseholes and they don't want to get labelled as diseased. I know some WG's still do bookings when they're unwell and the feedback system has just fucked things up if they feel they need to complete a booking when unwell to avoid negative feedback.