DH recently agreed, in principle, to proofread a new book for a European academic (ie not a native English speaker). DH is experienced in foreign & English language study and teaching but this is his first attempt at proofreading.
DH corrected a first chapter, dealing with grammar mistakes (in this he is very systematic and conscientious), but not focusing on style. In fact the style did not seem bad to him, although the subject is not one he has himself studied, so it is not easy to judge.
The lecturer has since written back, not criticizing the work in any way and expressing willingness to pay, but mentioning that DH had not made a great many comments. He says that he had not thought his own English so good, and had expected there to have been more mistakes! He adds that he may be being over-sensitive in this.
Do any proof-readers out there have any suggestions? Looks as though more chapters are coming DH's way but he's now uncertain how his work should proceed.