I've been doing "Mystery Talks" at libraries over the last few months as a way of letting librarians and patrons get to know me, and I have to admit it's more fun than work. After thirty years in the classroom, it's great to have audiences that actually want to hear what I have to say, and of course talking about mysteries will never bore a fanatic like me.
I feel a little guilty sometimes recommending Author A over Author B, because we all know that tastes vary, and Author B wouldn't have been published if someone didn't like her work. All one person can do, though, is say what she likes. My method is to define a sub-genre of mystery, like noir or cozy, give a couple of examples of the big names who write that type of thing, and then name three or four emerging writers. I try to name at least one that I've read and can vouch for, so listeners have reason to plunk down their hard-earned money and buy the books. Others I include because they've won some sort of award or been recommended by people whose judgment I trust.
What makes me an expert? Nothing except forty years of reading mysteries, but I never claim to be the final authority. Often the audience adds to the list, and that's great too. I write down their suggestions as well, because, like them, I'm always looking for a good book.