I spotted an upsetting thread at the Google Webmaster Help forums where one website owner claims the same day after he fired his SEO firm, his site went missing from Google - completely missing.
He said:
I gave 2 months notice to a SEO company that I was moving my services to another provider. They were obviously not very happy and I was sent an email today saying they have stopped all work and have cancelled the contract immediately. Two hours later I can't find my site in Google, when it was there this morning. This isn't fair as I was indexed before working with them. Can they do this? Could they have de-indexed my site? How can I cancel that request? My business relies on the internet for clients... I am desperate!
Can you imagine?
What did the SEO firm do to get this guy's site out of the index so quickly? Well, it depends on what access they have. They could have blocked spiders and issues a removal request via Google Webmaster Tools.
If you are firing your SEO firm, you need to make sure they do not have access to your site, your webmaster tools login or anything that can harm you. The SEO firm that the website owner switched to, should have warned the client that this can technically happen - although, not everyone thinks how evil people can be.
We've seen some SEO firms threaten to ban your site if you leave them or don't hire them. And we've seen SEOs take revenge when their clients scam them.
Let this be a lesson for both website owners and SEOs, be careful and tell your new clients to be careful.
Forum discussion at Google Webmaster Help.
Update: The support from the SEO community to help this person has been tremendous and I hope the site becomes relisted shortly.