You had me grinning the whole time I read your post!
I laughed out loud when I read:
I was certain that my role as ‘undercover shopper’ would be found out and I would be asked to leave, with dozens of genuine patrons looking on in outrage.
The image of a host of library patrons being upset about anything other than changed library hours or a copy of a book that the catalogue says is there but isn’t really cracked me up. Great to read that you had such a positive experience even with the guilty feelings and it makes me keen to conduct my own sneaky review. I’m sure my trench coat and large fake mustache can only serve to help me. You’ve inspired me to get all Carmen Sandiego on my victi- *cough, I mean local library staff. Thanks for the comment on my post too!