Most dealer valeters that I know of are only on just above minimum wage and get no sort of training in how to prepare cars. They are expected to clean 2-3 cars a day, so I would never expect standards to be very high.
Often dealers will get contract valeters in when they are pushed and pay them £30 per car. You can just imagine what sort of mess they make.
Given the choice, I'd take delivery of my new cars with all the transit proctetion in place.