It is extremely helpful for the experts if you declared whether you are interested in ‘light’ or ‘heavy’ editing before the editing begins, and you should specify the editing style accordingly. All the revisions will be done in a ‘track change’ mode, for you to accept or reject them, and you may expect the editor to insert comments and questions for you, when further clarifications are required.
In ‘light editing’, majority of revisions would be signalled as comments (e.g., a comment: ‘The meaning of this sentence is unclear. If you meant..., say…’), with no major stylistic revisions. Since there are many correct ways of conveying an idea, you may ask the expert to refrain from interfering with your personal writing style, as long as the message is clear. During ‘heavy’ editing, the expert introduces all the required changes (if you prefer for the text to be altered instead of having to go over editor’s comments and introducing the changes yourself). You may also ask them for more extensive revisions, e.g., simplifying the text and shortening the sentences.
Regardless of the editing style, you may ask the editor to justify any changes that they make to the text, as comments. You should remember that, ultimately, this is your text and you, as the author, will decide which comments and edits to accept or reject.