Some editing services I know especially the free ones from externship companies don't really edit your personal statement. I passed mine to an externship company and the guy there edited only two words. He just told me that it was a well-written PS. After I had my PS read by more reliable sources, I found out how wrong the content was (I didn't talk about me but more on about the professor that inspired me) and I had to overhaul and rewrite my PS. Be careful of these companies. They just use the "free CV and PS editing" to get students to avail of their services but the editing is inferior. I know a friend who had a similar experience in another externship company who offers free editing.
One of the best ways to edit a personal statement is to give the original statement to a relevant person and have them make suggestions. An example of this is if you are writing a personal statement as part of your application to graduate school, it is appropriate to ask a professor of the area you are applying to study to make recommendations for what to add and what to remove from the statement.
We specialize in editing personal statements for medical professions.
Since that time, the editors who work for me and I have edited hundreds of personal statements every year, giving each one the same personal attention and expertise that I had devoted to and learned from my friends and wife. It is out of this experience that we have established ourselves as leaders in editing personal statements for medical residency, particularly for IMG applicants.