My experience as a secret shopper at a medium-sized library one Saturday afternoon did not go so well. I was directed to a specific staff member because that staff member "liked to read a lot." I mentioned that I was new to reading mysteries and needed some suggestions. I was taken directly to the new mystery book shelf and told that would be a great place to start. I felt like I was about to lose her so I mentioned that I wanted a whodunit type of book with dark humor. She picked up on the keyword "dark" and suggested Stephen King and another well known author, both of whom are dark but not necessarily in the murder mystery genre. I described the tone I was looking for by relating the plot of the movie Heathers to her, and it didn't seem to be of any help.
At that point, I was taken to the OPAC and given instructions on how to use the advanced search features to narrow down what I was looking for. I told her I would give it a try, and she walked away offering to give any further help if I needed it. She disappeared without making sure I found anything of interest.
I wasn't all that surprised with this interaction because something similar happened to me on a reference assignment for another class. They were more concerned with teaching me how to find things on my own, but I was not given any in-depth, professional knowledge on the nuisances of doing so.