It's hard to say when the Barnes and Noble manga sale occurs. Sometimes it's announced on their social media or in-store flyers. Keep an eye out for those!
I'm not entirely sure as it could be various things. It might be a side story related to a story about love that is somehow for sale, perhaps a relationship that has a transactional aspect to it in the context of the story.
It could be about various things. Maybe it's about the different pets available for sale on an online platform, like their types, breeds, and characteristics.
The pet sellers are also likely to be main characters. They are the ones who put the pets up for sale, so they play a crucial role in the story. They might have different motives for selling the pets, like making some extra money or finding better homes for their pets.
Specialized manga websites or forums dedicated to manga enthusiasts might have listings or recommendations for where to purchase 'A Lull in the Sea' manga. You could also ask for suggestions from fellow manga lovers on such platforms.