Acknowledging a librarian lets readers know that you followed recommended best practice. 

If you plan to include a librarian assisted search strategy (either as an appendix or in the text), please acknowledge the librarian by name.  Copying and pasting a search string, word-for-word, justifies an acknowledgment by name. Possible acknowledgment:  “We would like to thank (librarian) from ANU Library for her work on the literature search strategy for this review.”