Usually reporting even one or a couple (if in different sections) does the trick. Also going to user's profile and using the report function there to report the user themselves can be useful in situations like that.
(It looks like in this case it's all been taken care of already.)
Usually, it is sufficient to report one post - you don't need to report them all; this should identify the miscreant to the mods and, once they have been alerted, they should be able to deal with him (or her) after that.
Yeah... all you need to do is report one of the persons spam posts and it does the trick.
What does help is if multiple people report a post. That helps get our attention in a long list of reports pending. So if you see a spam post and you are thinking others probably already reported it, go ahead and report it anyway.