by the sf is simple, even for a high school drop out. If he can't figure that out, how's he going to comprehend mixing a hydroforce!?
Determine what you want to make, pick a price per sf.
The 40-50% rule above will give you a rough idea of the carpet in a house. Take the total square footage and subtract 40-50% and that gives you the area of carpet. It seems weird but it works.
Determine the fraction of the room is open of furn if only traffic areas are going to be cleaned. Charge that fraction of your sf price for that room. Ie 60% of the room is open, take 60% of 50cents, ie 30 cents. If they can't figure that out, next.
In home quotes work great for closing, esp as a owner/operator. No surprises for them, none for you.
If you need a way to separate yourself from SS etc, you have to do something different. When they ask what makes you more expensive, you'll have an answer. If you price the same and clean the same, you are the same.