Don't know why you would have a problem going upstairs, common sense to tell customer you need to ensure all doors and windows in the house are closed to avoid drawing unwanted dust all over the house.Any self respecting decorator will seal up the doors if he's about to do a load of sanding and allow for it in his quote.
You keep digging Boss!
Not really, we have only been told one side of the story, the customers.
Was the decorator supposed to sand off the doors and frames, if so how could he manage it with the doors being sealed off, the story appears to have changed on several accounts, (Doors do not fit etc) and sounds rather exaggerated
I have been in this business long enough to realise that not all customers are on the level, and the trend of TV "Bodge it Builder" programmes can make accusations against the workman very "one sided"
If I am working in a ground floor room, there is no reason for me to go in Bedrooms/rooms on the upper floors without permission, this opens up all sorts of allegations.
Trouble with common sense is it's not very common.