Company writers do not have this liberty since it is the company that sets the price and often, do not inform the student that single spaced pages cost more.
In my experience, essay companies always disclose (somewhere) how many words they provide per ordered page. When customers order single-spacing, it's usually their attempt to "specify" their way around the company's word-per-page guarantee to get twice as much writing without paying for it. Whether it's ordered that way deliberately or because they genuinely don't realize that double-spacing is standard throughout the industry, the company will usually simply send a message explaining that a single-spaced 5-pg project is charged as a 10-pg project, but that formatting it in single-spacing is no problem. Then, the customer has the option of issuing supplemental payment, shortening the project, or canceling it.
One may have atrocious spoken English skills but near perfect English written skills because there is time to perfect the witten language.
I'm sorry, but I have to disagree. It's easier to speak a foreign language -- and, for that matter, even your own language -- than it is to write in it. However well one speaks any language, one usually writes less well in that language. Plenty of colloquialisms and idiomatic expressions that are fine in spoken English cannot be used (or are considered glaring mistakes) in writing. Writing also exposes all sorts of mistakes that don't really interfere with understandability in spoken conversations; and writing also exposes punctuation mistakes that aren't evident in spoken English.