tedster - 5:39 pm on Aug 1, 2010 (gmt 0)
Here's one type of situation that might be incorrectly analyzed as a toxic link penalty:
1. The penalized site is hosting parasite links.
2. The hacker-spammer has pointed links at those pages to boost their ranking power - for as long as it takes Google to spot and devalue them.
3. Such backlinks then hang around indefinitely and look toxic.
4. But the actual penalty is caused by the parasite links hosted ON THE SITE, and not by the toxic backlinks in themselves.
A while back there were some black hat services that offered to take down a site's competition (for a hearty fee, naturally) and they seemed to rely on a creating a BIG pile of toxic backlinks to do the job. I haven't heard of that working for a while - Google seems to have handled it.
Then use a custom 404 as a new sitemap to acknowledge the change to those who were linked/bookmarked to the old page
Of course, this would break the link juice flow from legitimate backlinks, at least until they changed over. If there are significant legit backlinks, I'd be very hesitant to change the URLs of their target page.