Q.   Why do some carpet cleaners charge by the room and others by the square foot?

Short Answer:   Charging by the room (or area as it is now referred to) makes it simple to quote prices over the phone.  This method is often used when a company has a base cleaning price and lots of Up-Sell options for the customer. 
Long Answer:   Charging by the Square Foot requires the technician to measure the carpet to be cleaned. This is nessisary to determine the exact price but it also allows the consumer to only pay for the areas needing to be cleaned. So if for instance  the consumer  only wants the high traffic areas cleaned, they won't have to pay for the whole room.

Delta Steam-Way
The Premier Carpet Cleaners in Elk Grove