When answering a question, is it okay to post a link (or links) to information on other sites? I didn't see any mention of this subject in the FAQ.
This site should strive to become THE canonical source for home improvement information on the internet.
As such, the text of the answer (the information contained on this site) should be as complete as possible. Currently 64% of your traffic comes from search engines. Remember that any information contained on the other side of a link will not help bring people to this site.
Certainly include links for proper attribution where you are quoting a source, but the best answers are those that try to improve on that data and provide the best possible expert answer. A link is useful if you are directing a user to further information outside the scope of the question. But simply saying "Your answer can be found here [link]" does nothing for this site.
Stack Exchange sites tend to rank very high in search listings. Consider for a moment that anything you write can soon become THE canonical answer for that information on the internet. Take advantage of that opportunity.
provide context for the link -- if I click this, what will I get? What is on the other end?
quote the most important part of the content with the link. You shouldn't have to click through to find "the answer", the most important bits should be there without requiring you to click through to have a complete answer. Also, sometimes links are inaccessible and sites go dark!
This site may be the concern of Stack Exchange, but the users want information not just the enhancement of the vehicle itself. If there is a good answer elsewhere, let's use it and give full credit to the creator/provider of that info. (Copyright law and fairness also encourage this)
No, we don't want the search for answers to be a daisy chain of go here, then go there then follow one more trail. Also, we don't want to send people to dead links on sketchy sites. But use of reliable sites that directly answer questions makes this site a portal to the good info. That is also worth something.
I agree that complementing info on other sites, with personal experience, insights, synthesis may be the best of all possibilities, but let's not avoid the links when they directly meet the goals of the users.
Regarding product links, go with whatever page has the most useful, relevant information. The vendor pages have the benefit of being authoritative, but Amazon can win out due to accepting user content such as reviews, photos, videos and edits to product info.
On the otherhand, if it looks like someone is just trying to promote their own blog or web store, go ahead and flag it as spam. (If you're unsure try looking at their profile to find their other questions & answers to see whether they're doing it repeatedly.)
On a related note, Amazon links are magically changed to use Stack Exchange's Amazon Associates account so there's no benefit to anyone spamming links using their own Amazon Associates account, and it helps support the site in a very unobstrusive way.