I think certain shopping questions that meet some fairly clear criteria should be allowed.
First off, I am not aware of any ongoing issue with poor quality shopping questions (or really many shopping questions in general). It may be that I've simply missed them (I vaguely recall seeing one or two in my time here), and, from Gilles' answer to this question, at least one question was closed and deleted. Regardless, it seems unlikely that allowing some form of shopping questions would suddenly flood this site with low-quality posts.
There are also two types of "shopping questions": those that apply to people looking for where to find specific, hard-to-find products that they've already identified, and those who are looking to identify which products of a specific range of similar products best meet their criteria.
The second category is well-addressed by Gilles' answer above:
- Questions about different versions of a work: if there are artistic differences, then this isn't a shopping question, it's a question about different-but-similar works, and thus on-topic (it might be undesirable because it's subjective and argumentative, but that's a separate issue).
- Questions about different editions of the same work: I see several subcases.
- If there is no objective difference between the editions: why was the question asked in the first place?
- If there is an objective difference (e.g. different sets of short stories or different languages on a movie), and the answer is readily available on a reference site (e.g. ISFDB, IMDB), the question isn't particularly valuable (close as general reference?).
- If there is an objective difference, or at least easily available material suggests that there is one, and it's not easy to find out what the differences are, then I think it's a good question (example). I don't see why it would matter that the work is not available for free.
The other category, those questions that know the product, and are looking for where to find it, need to meet some specific criteria.
The first is whether it meets the general topic of "sci-fi/fantasy". This one seems pretty easy to me:
- is it a product which depicts, in some form or another, a work of science fiction or fantasy?
This includes any book, photograph, recording (audio or visual), drawing, sculpture, or any other medium that depicts all or part of a specific science fiction or fantasy work, with the intent of making it clear that the depiction directly relates to that work. Examples could be anywhere from specific editions of a story or collection of stories, published interviews of authors or other individuals contributing to a work, authorized reproductions of characters (action figures, promotional stills, sculptures, etc.), or promotional products related to the work.
Note that I believe this should include specific categories of science fiction, in addition to just specific works (e.g. "vinyl radio plays of science fiction pieces", "autographed action figures from Firefly", "signed first-edition fantasy novels written from 1910-1920", etc.), so long as they meet the next criteria!
The second addresses "not constructive":
- Is the product difficult to find?
If you can find a dozen or more current sources through a quick google/ebay/craigslist search, then its not a valid question. If it is available from a single mainstream chain distributor (e.g. amazon.com, direct from Disney, etc.), it is not a valid question. If the only sources easily found appear to be of questionable legality (torrent sites, etc.), it may be a good question.
Another criteria to consider is "too localized":
- The question cannot specify that it is only looking for shopping for within a specific region.
Normally, "too localized" doesn't preclude questions relating to specific geographic regions, at least on many SE sites. However, for our purposes, given how rare and niche these shopping questions should be, I don't think a question that asks for brick-and-mortar stores available within the Berlin metropolitan area are going to be terribly useful. It is possible that answers may be restricted geographically (e.g. "I know a comic store in Hobocken, New Jersey..."), but if the asker is only interested in sources physically located in Japan, they'll just have to hope that one of the answers is usable.
Note that questions that are restricting the search to a specific region should be edited to remove the restriction when possible, rather than being closed outright.
If a question meets all of these criteria, the question should be on-topic for us.