Confirm the surface first
Block paving, concrete, natural stone, decking and rendered walls do not all require the same approach. Send wide and close photographs so the material and condition can be reviewed.
Ask about joints and drying time
Pressure washing can disturb sand between blocks. Ask whether re-sanding is part of the proposed work and when it can be completed after the surface dries. Stains, drainage and nearby doors or vehicles should also be discussed.
Provide access details
State the approximate area, outside water availability, drainage route, parking and anything that must be protected or moved.