Dont quote over the phone.
Firstly. It doesn't appear professional. You are a professional remember. Your customers are expecting you to be professional. So behave professionally to their enquiry.
Secondly. Someone throwing together a quote over the phone without viewing the property doesn't come across in a good light, even sub-consciously.
Thirdly. You need to assess the customer. You need to read them, their body language, their attitude and their responses to your questions.
Fourth. You don't want to pick up work where there is dog-poop scattered liberally around the place. If their is forget the job immediately. They're filthy, unhygienic people who don't warrant your time.
Fifth. You need to imply who's 'running the show'. Its your business and your work, you have guidelines they need to be aware of. You tell them, face to face, whats going to happen. Such as possibly texting them the night before if their back gate needs to be unlocked, how to pay, what to do if they're not happy with the quality of the clean.
Sixth. You can assess immediately if their might be the possibility of other work from them, such as gutter cleaning/clearance or cladding cleaning. You could sell them this on the first visit. You'll be viewed as efficient that way.
Seventh. Businesses that impose themselves indicate a level of professionalism, being in control and that you are experienced and know what you're doing.
Eighth. Customers like confidence.
Ninth. Dont quote over the phone.