What exactly makes a "shopping-list" question a "shopping-list" question?

Question

Always eager to learn about the Do's and Don'ts of every SE site I frequently visit, I have to admit I'm a bit confused about Ebook.SE's handling of "shopping-list" questions.

I once asked the question "Some classic literature is available for free - but where?" which was ruled off-topic as a shopping-list question. After a bit of thinking, I managed to wrap my brains around that and even agreed on the closure by casting a close-vote myself.

But then I recently stumbled upon the question "Where can I source images for ebooks that are not restricted by reproduction limits nor dpi?" and I started to wonder why no one seems to care that that question is a shopping-list question too. I mean, how much clearer can I don't mind paying for images as long as the prices aren't exorbitant. get?

As a result, I'm a bit unsure (better: worried) that there might be something in relation to shopping-list questions in general that I don't quite understand just yet. What makes my reference request off-topic, while a clear "shopping" question is on-topic?

It would be cool if someone would find the time to explain why both questions are handled different, because I don't want to flag any questions wrongly just because I might be missing something important. So, what exactly am I missing? Where's the difference? Why are some shopping-list questions on-topic while others are off-topic? Is there a special definition of shopping-list questions I should learn about?

Or, trying to wrap it in a single question: What exactly makes a "shopping-list" question a "shopping-list" question?

_{(Nota Bene: I neither want my question to be re-opened, nor do I want that other question to be closed. Pls think of them as examples.)}

Answer 1

I think they are both shopping list questions.

The Stackexchange position I think is best explained in this question on meta stack overflow.

The main issue here for us is

They are open-ended; there is never one perfect answer to them.

However I think we probably should be a bit more lenient that say Stack Overflow as some questions ask for a product will allow a focused answer. For example this one asking for a reader app on a particular phone as there probably only one or two possible answers. However being inconsistent asking the same question for an iPhone or Android would get a large number of answers and so I would suggest it be closed.

Answer 2

Another thing to consider is that the first question may be easily answered with a simple search, while the second one is a bit more difficult - at least, when I published my first book in 2011 I had to dig a lot before finding good sources.