This clearly is foreshadowing their first kiss, where they'll then swap bodies.
Wrong manga?
Why is Miss Sunflower suddenly selling new books for less than she buys used books for?
Miss Sunflower is good at books, not business.
Considering Miss Sunflower doesn't have an actuve lifestyle so her expense would be very low. She owns the shop and the living quaters so she's not paying rent or maintenance fees, therefore besides daily living expenses she really doesn't have to use money for anything else. All the income from the shop is more than enough for her to buy new books. She also explained in one of the earlier chapters that she also goes to old bookshops to buy books she likes to read and would resell it when she finished. Assuming she keeps the books very well preserved, a new book that she bought for $30 could be resold at $28, and the next time she goes to buy books and she sees the book at $25, she could take the price down to $23 and she would still be able to sell it. After a while her bookstore would be known to have good quality books for the cheapest price so more people will come to buy, since there is only one copy per book, those looking for a certain new book will likely come more frequently around it's release time to buy it after her. It's actually not a bad idea, she effectively manage to combine both her cost of leisure and cost of stock into one.
That is ofcourse assuming she is actually giving her bookstore a competitive edge.
Anyways...sorry long post. Just wanted to say I live this story, I love everyones relationship with each other i only wished there was more yuri. I feel that the story is more about Miss Sunflower and Matsuri are really only going to help each other move on from their current static life, I'm afraid at the end of this journey, Miss Sunflower will get over her previous namesake and sell the shop and move on with her life, I get the feeling she will leave the country or something. While Matsuri will enter University, free from her fears and with the courage and confidence to reach her life potentials and really make a go at a successful future. I fear that years down the track when they may possibly meet up again, it would be friendship only between them.
I was(am still) a hard Nana and Marimite shipper and had my heart broken.