It depends on what the retail store sells.
My student job was working at a bookstore. Our customers are a special breed, I think, but there are some generalisations that can be made.
I sometimes heard (albeit very rarely) my coworkers ask "Fiction or nonfiction?" But that didn't necessarily increase sells from our observation and discussions we had about this approach. But some supervisors pushed this concept to "get the conversation going". Truth is, you need to be yourself when facing a customer. There are as many different customers as there are personalities in a workplace.
It's true that it depends on your customer. But most of them want to be left the heck alone. So what approach worked for me?
Asking a casual, open-ended question or making a comment about them. This allowed me to gauge whether this person wanted help or not. It worked most of the time. It's all about making the customer feel comfortable with you.
Casual questions/comments I would say:
1. Oh! I've heard a lot of good things about that book. Apparently [insert author/interesting book fact that doesn't reveal much of it]
2. Hey, how's it going?
3. Jesus, is it still pouring out there?
4. Hey, watchoo lookin for?
5. Okay, it looks like you are trying to find something (when they appear lost and are going in circles in place)
6. Hi. (simply acknowledging them -- you can tell they don't want to be talked to if they act distracted, make an effort to avoid eye contact or walk busily/quickly away from you)
In the end, every customer will find an answer to get out of any question, full stop. So don't try to fake it.
If they are already holding a book, that is the easiest target, because you can make assumptions about that person and start a genuine conversation.
Another is actually a close-ended question:
*What section are you looking for?
The trick there was the follow-up comment/question. Say they said "history". Okay. "Oh, the new Trudeau biography just came out and the biographer had a bunch of access to documents and files which no other person has ever looked at".
If they said "Not sure". A chuckle then "Is it a gift or for a special occasion?" Sometimes customers don't know what they are looking for, actually. You need to have an honest demeanour. In the end, I was always honest with the people I dealt with and had people visit me to talk to me. Probably half of us had degrees or were in the process of getting degrees so we had our own specialisations. I had a bunch of people who remembered me and we would recommend books to each other and just chat. I spoke for a couple of hours to customers about philosophy or Latin American literature and history. A few were extremely impressed with my knowledge and the same occurred with my other coworkers.
This building of rapport is the best thing, I think. Almost like selling is an afterthought. Humanising the transaction is better, I think. And something that I feel is lacking in a lot of customer service. We're all humans. All of us have our bad days.
If there was a customer looking for something I had no idea of, I'd think of someone who did know. And would tell them honestly, "Actually, I have no idea about that, but I think my other coworker might. Let me call her/him". If no one knew, which happened sometimes, we would try to help them the best we could. In a lot of these cases, we had no solution. But the customer was happy that we at least tried.
If we never stocked a particular book, we'd recommend them to another bookstore. We had a binder filled with different bookstores. Most were surprised we did this.
Despite all of this, this bookstore is one of the most hated in the city I lived in (if not the entire country). Poor management, too bureaucratic, and old habits. Plus, inconsistency between other locations (it is a chain bookstore).
The absolute worse thing about working there had to be PROMOS, as in, the giving out of flyers/coupons. Very, very, very, very few people like being handed stuff. And many customers knew we suffered (they could see it in our faces), so a minority took them out of sympathy. The biggest problem with this was that when giving the flyer there was an unspoken time frame to hand and explain the promotion. And this time frame was about 5 seconds or less, and usually there was a caveat to a promotion that required more time to explain, because it seemed like the nature of marketing was to purposefully create convoluted/complicated scenarios where the promotion would apply.
Anyway. My two cents. Sorry, it was an unabridged/unedited and not proofread response.