Can you take someone down?

Is it possible for someone with outstanding knowlegde of SEO and stuff to do something to affect someones 3rd party business in terms of serps.

I recently wrote a review on a product, which was not overtly positive and my serps have all been reduced by 95%

Does someone have the power and if so, what is the point of doing a review on someones product if their are grave consequences?

It's possible to do things off site that impact another site, yes but if it's a site like Wikipedia then you're not going to effect it.

As for the review and rankings drop, unrelated i'd say. It "may" be possible someone read the review, found faults with your site and lodged a webspam report and you were manually penalized.

so a webspam report does not have to be proved... seeing as I am not doing any? do they just take someones word for it?