Consultants often rent a desk (and pay for it) in client premises. If you do so, think for a while before leaving in the evening what your desk tells about you.
Yellow post-it spread everywhere could suggest you are a 20th century consultant (now we are 21st guys) who never heard about PDA or smartphones with reminders you can rapidly synch with your PC.
Paper sheets spread everyhere could suggest you don’t care about Amazonia forest nor about confidential info. Moreover, if you left them on the desk then it should not really matter if someone take them, shouldn’t it.
Glasses, bottles, rubbish in general do not only suggest you are not the right guy to marry with, but also you probably don’ t really care about keeping order. So what if your client is thinking to give you access to a lab or delicate instruments desks?
Some clients could also consider your “leaving the stand by light of the monitor on” as if you do not really care of the fact he is spending for you.
In the end, never forget: you are a guest for your client. Your interest is being invited again.