Everybody wants to know and almost nobody asks first. So they ring three landscapers, get three wildly different figures, and pick in confusion.
A rough range on your site — per square metre for paving, a starting figure for a full build — does three useful things. It stops the enquiries from people expecting a garden for eight hundred pounds. It makes your quote land as reasonable rather than shocking. And it makes you look confident, which is worth more than the number itself.