If the Service decides that the requested pagesize was not acceptable and uses a different page size to the one requested (I.e. the caller put in millions to try and "dump" the database, and service decides that it wants to only accept 100 as highest number) then the caller has no idea what the actual page size used was.
(Except maybe to see that there are more pages of data, and that the number of items is different to what was expected)
If the Service decides that the requested pagesize was not acceptable and uses a different page size to the one requested (I.e. the caller put in millions to try and "dump" the database, and service decides that it wants to only accept 100 as highest number) then the caller has no idea what the actual page size used was. (Except maybe to see that there are more pages of data, and that the number of items is different to what was expected)