You should also consider keyword variance. If you are trying to optimize for the phrase "carpet cleaning", you could have the phrase 'carpet cleaning" a couple of times, then have "cleaning carpets" once or twice, and then have "get your carpet cleaned", and a sentence containing the phrase " ... a clean carpet ..." etc.
You are more likely to get ranked well for the target phrase if you mix it up like that a bit, rather than just repeat the phrase "carpet cleaning" several times.
There are, of course, many other factors that the Google search engine considers. Keyword density is not considered to be as critical as it once was.