I often mention that in my reporting comment to try to get spam mega threads locked. I'll report spam posts within the last 7 days so spammers won't get paid for them, and then I'll report the OP's post stating something along the lines of "Spam mega-thread, x number of spam posts in the last y days reported for deletion. Please consider locking." You can even do it over the course of a few days or a couple of weeks if the thread isn't terrible but keeps filling up with spam - I just search https://bitcointalk.org/index.php?action=reportlist;mine for how many good reports I have in that thread. If it's >50 posts in the space of week, that's a pretty sure sign the thread is a spamfest.