HELP Google Penalty - How do I figure out what it's for?

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Hi Guys,
I have a website nelsonvacuums.com.au that is about 18 months old. It went so well on a standard shopping cart solution that 9 months ago we started talking with a CRM provider. Now it took many months to get it off the ground as we have a "very Involved" set of products. 3 months ago we went live and initially we had a good result but then BAM we have gone into free fall. As a result I have begun to be active learning all I can about seo etc etc and as far as I can tell we have really done nothing wrong to get banned. When I use a rank checker we do not register at all with google for ANY of our keywords.

My big question is how do I figure out what it was that got us penalised?.

We have never done link exchange, link buying, hidden keywords or anything else that is regarded as being black hat. In fact I personally have made all links from relevent forums.

So please collection of almighty GURU's help me out!

[theSEOguys]

Unfortunately, you will not be told what you were penalized for. Did you buy links? Did you outsource and link building and have thousands of links applied in a short period of time? Do you have any hidden text? Any cloaked pages?
One of my sites was penalized last year. We oustsourced some link building to a foreign country for a "boost". Unfortunately, the boost got us a 30 day penalty. We applied for a request for reconsideration through Google's webmaster tools. We told them what we did, what we think we might have done, admitted we were wrong, and won't do it again. The process was fast and fair. When we came back, we applied some proper SEO, and came back further up the rankings then ever. Watch the video for a better understanding.