I did a bus depot office last month, it was really bad so I vacced it, then rotary scrubbed it with a stiff brush, then vacced it again.
the dust the scrubbing loosened was incredible.... it was like a dust storm we did this 3 times until it stopped creating the dust storm.
Then I presprayed M/S, then again scrubbed this in with the stiff rotary brush. I then went across with folded terry towels'
it came up really well....... but I think we could have walked away after just scrubbing & vacuuming and they would have been happy, it made such a difference.