The first question most consumers ask is:
"How much does it cost to clean...?"
The answer really doesn't tell you anything about how they clean, how well they clean, what method, what procedure, do they move furniture, etc etc.
Better questions to ask are:
These will give you a good idea about the company's experience and their technique.
Also, ask if they provide an in-home inspection and provide a written quotation before any work is done. A written contract beforehand can help you avoid being responsible for any "extras" that you may have assumed would be covered by the cleaning service. No surprises.
I would say the best question you could ask is:
"What do you do for what I am paying you?"
I like this question better because one, you won't lead them to giving you the answer you want to hear, ie do you vacuum? and they answer Yes just so they can get in the door.
Two, usually they will tell you exactly what they "Normally Do", ie what they're basic procedure is. Anything beyond this that you would like done you can expect to pay extra for.
By asking this one question you can more effectively compare companies "apples to apples" rather discovering you've been misled once they arrive at your door.