I would assume people buying volume 1 on day 1 are people aware of the series already from the magazine and maybe it's just me but even if I like the opening bit if I know it's going to go downhill (especially within the next couple volumes) I wouldn't bother picking up volume 1.
1. I’m sure a lot of the people buying volume 1 are people who read it week by week in the magazine and are at least somewhat caught up. So they probably like the series as it stands and likely won’t just stop buying when volumes 2 and 3 are out.
2. If the series ends up being a hit and selling well, not everyone, but a lot of people who were saying the series sucks now will switch up and act like they never thought the series was bad. That it you’ll see a lot of “actually, now that I’ve caught up I think it’s pretty good now”.
Don’t have specific fingers to point as to who does this and who doesn’t because I don’t pay attention that closely. But I noticed that with all new series a lot of ppl base their opinions on the TOC, sales, and/or the opinions of every one else, and you see that the overall reception shift whenever they see they it’s popular.
Same vice versa. Some ppl will say they love a new series chapter one, but as soon as it places last in its first TOC placement you’ll see ppl constantly talk about how it’s bad now.