See? That's what happens when you don't have a sacrificial goat. The Google Gods go hungry and take it out on you.
Seriously though, any percentage is not good (IMHO), if any of an SEO company's clients are hit by an update, it just shows that they used shortcuts. There are jobs being done at fiverr, marketing forums loaded to capacity with people selling SEO "products", and most times, its really just not worth the money you pay for it. In most situations, you have these companies outsourcing to these people and it can't always be controlled. Nine times out of ten you're stuck with links in bad neighborhoods, spammy comments placed on blogs and all the money you paid for a quality service has gone down the tubes.
SEO is not an art, its a lot of reading in the beginning and a lot of updating with trends etc. But its something anyone can do if they just follow the right guidelines.
And get a herd of goats... you can never go wrong with those.
