The service
When editing, I address clarity, consistency, completeness and correctness.
It is quite likely that when I return your documents they contain queries for your attention. Most queries are requests for (missing) information or clarification, and they serve to ensure the integrity of the manuscript.
What I don't do
I do not check the truth of what is written. You (or your writers/subject experts) are the expert(s) in your field and the content of your documents, and the responsibility for factual accuracy lies with you.
However, where I consider it necessary, I will check what I can and seek information to try to clarify the meaning of the text, and I will query if I think there is a potential factual error.
Of course, obvious errors are corrected.
Tracking changes
For transparency I use the 'Track changes' feature wherever possible: this way you can easily see the changes I've made.
If you will be returning any documents to me, this feature is the means by which I can also spot any changes you make. Therefore, it is vital to keep this feature switched on and to make any changes within the text where necessary (rather than accepting or rejecting changes before the document is finalized). Otherwise - unless all the changes since I returned the document are limited and fully disclosed - I cannot easily see where any changes have been made, and, indeed, I may not find accidentally or newly introduced errors.