There seems to be some consensus that shopping requests are often off-topic, particularly those that ask for recommendations for products rather than recommendations about what to look for in products:
A healthy portion of the questions which have currently received votes to close seem to fall under this category.
Unfortunately, the vote-to-close page only has one category in the "Closing > Off-topic" section: "General health and medical advice". Would it be possible to add a "shopping requests" category, too?