Hey all, just to chime in on this one with a few thoughts.
The bottom line is that overall, we don't want to have folks posting here simply to build links to other websites. They're pretty easy to spot in that they usually make a point of including a link in their very first or early topic or reply to a topic or post with a link to a competing service or commercial product elsewhere that they either have an affiliation with (affiliate link for example) or some undisclosed relationship. These in my view, should be removed without hesitation and the poster set a warning by a moderator or admin.
Personally, I'm happy for us to link to whatever resources we feel adds value to whatever conversation we might be having. If another forum or resource is citing a view that is complimentary or useful to the discussion then it makes sense to reference it, provided that we don't have a suitable reference here and that the person referencing it is a trusted user of good standing.
There will of course be edge cases and we wouldn't really want to have a situation where a poster kept on linking to the same place as that would look a little fishy
As for complaints about shops or products or other businesses the general rule is that they are not really welcome, especially if they are ranty or defamatory. So in short, any posts that cross the line will most likely be edited or deleted.
Hope that helps!