More than that, Jakey.
I find it best to mention a sqm price then measure up properly.
Show them your workings and round down.
Usually, customers don't know how many sqm they've got and £x psm sounds fine.
Then once you've done the maths in front of them, even if it seems expensive, they usually say ok.
Push the fact that you're not a pikey (if you're not) that you'll re-sand if needed. Little extras that you throw in.
Encourage them to get other quotes.
Tell them before they do that you won't be cheapest but 'there's a reason for that
'
(Don't go down the route on CIU of 'what would you charge?' It will range from £10 to £1,000 and all the Walter Mitty's, willy wavers & beer money boys will be out)