As a rule, we don't get questions that ask for shopping recommendations here. We get literature recommendation questions sometimes. That's different.
“Shopping question” to mean questions whose answers are likely to involve pre-existing things (a piece of computer hardware, a software package, a book, etc.) is an unfortunate piece Stack Exchange slang. It essentially has a pejorative meaning. By using this term, you are driving the discussion towards a specific answer — “if you defend shopping questions, you're bad”. Please refrain.
There are at least two distinct types of questions asking for literature recommendations:
- Questions asking what paper to cite on a given topic. These questions usually have an answer which is a single paper (or “it's folklore”). A significant fraction of our reference-request questions are of this type. While I tend to find these questions boring, they do not raise any particular moderation issue.
Questions asking what to read on a given topic. These questions are problematic to moderate, because they tend to degenerate into lists of items. Stack Exchange has no problem with recommendations — we just want them to be constructive — but Stack Exchange is not good with polls. The problems with questions that call for lists (“what books should I read?”) is that they tend to attract answers that say “you should include this one book in your reading”, which doesn't really answer the question. An answer should recommend a curriculum, not a single item. See What about list questions?
We have no ban on questions asking for a curriculum, and we should not have one. The usual quality control does apply, of course. If a question is too broad (lacking information about the scope of the topics that should be covered), or primarily opinion-based (lacking context to rate which books/papers are most relevant), then it should be closed. Furthermore, we should apply quality control on answers: please downvote and flag answers that recommend a single item rather than a full reading list.