Is the area furnished?
How many people work in the office?
How old is it?
When was it last cleaned? If yes, who by?
What vacuum cleaners do they use?
Does it all need to be extracted?
What window do you have to carry out the work?
Is it air conditioned?
Will they require extensive paperwork RAMS, COSHH etc?
How long will they take to pay you?
Would they benefit from planned maintenance?