For many things in life, there is a strategy that says: If you're going to do this thing, then the one thing you must do is this other thing.
If you're a bookseller you might subscribe to this strategy for aspects of your business. Books are so incredibly varied in so many ways that it is tempting to limit yourself to some categories or one category, to one or two sales scenarios, to a look. Maybe you only sell in a bookstore and school book fairs, or only on the internet. Maybe you have a children's bookstore, or sell only new books or only used books. I know of at least two booksellers who sell only books about trains. Imagine a hardware store that only sells nails. We are in an interesting industry.
Then there are the general bookstores, the big independents that sell everything. They sell new, used, bargain, non-book, calendars, services, and whatever they can make work. They sell online, in bookstores, mail order, at expos and fairs. They do phone sales, business to business sales, bulk sales, sidewalk sales, school sales.
These are the bookstores an indie bargain book sales rep is going to have the most luck with. They tend to have buyers that specialize in or focus on remainders and bargain books. Those buyers tend to buy deep and wide, so that a wholesaler with a large inventory comprised of books in many categories will see orders from these buyers for at least something from most of those categories. These buyers know what their customers are looking for.
They also usually know when they don't know. If a sales rep says that a title the buyer just passed on is selling well to many other buyers, the buyer might reconsider. However, they still have some of those old strategic limits when it comes to categories. They might avoid books about computers and technology, or health and fitness, or travel or business or, weirdly, children's. As with any buyer who says they are avoiding a category, they will see something that works in one of those shunned categories and suddenly buy a ton. It's the exception that proves the rule.
In my completely biased opinion, buyers should give everything a chance. Put books in front of your customers before deciding you know they won't buy them. I hear so often the surprise that something sold that just should not have. We know what our customers buy only because they buy what we buy.
However... If you're a general bookseller and you're going to buy only one category for your bargain department, make it children's, cooking, or art. Children's bargain books sell like ice cream at the beach. Parents know real books are important to their children's development and children know their parents have a hard time turning them down when they want a book. And, oh yes, kids love books. Cookbooks sell no matter what, but they tend to sell better as bargains because of the original high list price and because the customers buying them know they will get some very rough treatment at home.
Why art? It can be a hard sell. They are expensive to begin with and mostly still expensive as bargain, but they have the increasing appeal of books which really just work way better as real books than as e-books. This is also part of the appeal of children's books, but much more so with art. Paging through an art book, be it a monograph or a technique book, is an unbeatable and unique experience. So, if art is on your shun list, make a few exceptions on your next bargain buy.