There are always a few questions that are valid questions but just off topic for this site. Product recommendations are a great example. Apart from flagging and commenting so the user understands why it's off topic, is it proper form to also go ahead an answer the question?
For instance, here is a question asking for a book. I know of a great book I used and would love to recommend it but I feel that if I answer the question, the poster will have gotten what they wanted and thus the incorrect behaviour (posting an off topic question) is being reinforced.
Should we specifically discourage anyone from 'answering' blatantly off topic questions for fear of encouraging the improper behaviour?
Scenario: (I just watched November Man last night;)
Some user (new or old) continually asks for product recommendations, opinions, etc knowing full-well that the question will be closed within a few hours (and perhaps even their account flagged/etc). That user asks this question because he/she has a good chance that some person will answer the question with their opinion (perhaps even if they voteDown/flag the question). The user continues to repeat this process because although the questions are getting flagged/closed, the user is still getting what they want (albeit in a crude way).