How effective are Amazon's spam filters for product reviews?

How do we know who has made a purchase when reading through reviews? I feel like the verified purchase is a bit of a misnomer, and also it's probably being gamed by companies having people that work for them make purchases to leave good reviews....

I checked out on eBay with a guest profile. Can I still leave feedback?

I purchased an item from a small seller on eBay and they really went above and beyond. I'd like to leave them some great feedback, but I checked out as a guest. What are my options for feedback?...

Is it just my imagination or do Black Friday sales seem worse every year?

As time has gone on things have seemed more expensive to me with each passing Black Friday. Is it just my imagination or could there be a reason for this?...