In 2012 I was asked by Rayotec to work to remove a formal "unnatural link" penalty on their website from Google which was removed a few months later. I was not involved with their SEO beforehand. This included a disavowal of backlinks and a reconsideration request.
I've worked on multiple sites affected by Google ranking drops caused by various factors including the Google 'Panda' & 'Penguin' updates (not as a result of my work) as well as one with what appears to be 'Negative SEO' from a competitor. I've 17+ years professional experience - over 15 of which I have worked as an independent consultant.
If you'd like to contact me call me on 01252 757562 or email cwjbyrne[at]outlook[.]com .