While layering services do not technically modify the content as originally generated by a web author, some have complained that annotations are not approved by the authors and may be problematic. For example, comments may be inappropriate and offensive. A comparison to blogs is used by some in explaining this objection. Blogs typically allow the author to control comments. The author may prevent any comments or moderate comments before the comments are released to the public.
Hypothes.is is one of the first services I am aware of that offers a partial way to address this issue. I say partial because the technique is under the control of the individual who creates a group for annotating web content and not the author(s) of the content annotated. So, for example, a teacher could moderate annotations generated by students the teacher has formed into a group.
The system is straightforward. Annotations made by members of an Hypothes.is group appear with a flag when viewed by members of a group. Clicking this flag by a member of the group sends an email to the group moderator who can then decide if the annotation is reasonable or not and delete the annotation should this be necessary.