I agree with grey hat, but I think well reseached. I personally don't expect a penalization observing domain age and former links count. Anyway when the guy stops working for you (assumed it's all done with links) you should carry on some "minor" link campaigns!
Well said. blogs? - blocks, I think right? - Have to add some rubbish to be accepted by the DP system for a post. Just a question: What do you think about a site ranking first page for a high competition (more than 150.000.000 results) 2 word KW; domain age 2 years about; links: Google 4, Alexa 18, Yahoo 300+ whilst most of those 300+ are domain links, in reality it comes down to about those 18 Alexa links?
I think since those are tough keywords fluctuation would really happen, its not black hat since your site is still up in google serp if the guy got tough link that would help your site to stay longer on top that would be the time to make it stay longer but don't expect to stay on top for long because of the competition.