Q:

Is answering with a product recommendation considered spam, or something to flag? 

The problems with shopping list questions have thoroughly been explained already, but recently I've run into the opposite problem: a product recommendation as an answer. 
This answer is already very bad - it doesn't actually answer the question being asked, and it borders very near spam territory, even though I don't know whether or not the answerer has any affiliation with the source material.  
Even if all those things were accounted for, is giving a product recommendation like this inappropriate for an answer in and of itself?   Is it reason enough to flag the answer for moderation?   

A:

If reading a book might help you answer your own question, then I think recommending it is fine as an answer, as long as the contents of the book are described sufficiently within the answer to enable you to choose whether to investigate buying it further. 
Such an answer should not be flagged when there are options to downvote, edit and comment available to you to express any concerns that you have with an answer.   Flags should only be used as a last resort to call in the human exception handlers. 
I note that the user you suggest is borderline spamming appears to have answered 125 questions on that site and only one other time has mentioned the same book author: https://money.stackexchange.com/search?q=user%3A10613+howard
I also note that the same author has been often mentioned in posts by quite a few other askers and answerers: https://money.stackexchange.com/search?q=%22Clark+Howard%22
In other words, this seems far from spam and looks more like someone trying to be helpful to me. 

A:

On money.se, we get a lot of product recommendations in the form of links from new users who have never posted anything else.  The recommendations generally are valid answers to the question, at least in theory. 
Chances are most of them are spam in the sense that the user is just promoting something they are involved with or posting an affiliate link, but it's not generally completely clear-cut.  I tend to just delete those answers but clear any spam flags, and warn the user about self promotion. 
But this case is quite different: the user has 6K rep so must have posted plenty of other good content.  High reputation isn't in itself proof that the user isn't a spammer, but since most of our spam is drive-by it does at least mean that it doesn't fit the usual pattern. 
Looking at the detail, it's rather unlikely that the book recommendation is self promotion.  I agree it isn't a very good answer, but it doesn't feel at all like spam.