If all that's happening is fake good reviews and bots upvoting bad ones, it's not a problem if you take the approach I do and think is the only correct one:

1. Only read the bad reviews

2. Ignore the fake or irrelevant bad reviews

3. Ignore the good/bad ratio

Of course, if people are good enough at faking bad reviews, then there is a problem, but I like to think I can tell, and it isn't something that is practical to scale.

The whole idea of treating reviews as some sort of voting mechanism that determines what you should buy makes no sense. The way I look at it is, is there something non-obvious that is a dealbreaker? That's what reviews are for.

If I was running an e-commerce site, I'd simply not allow good reviews at all. Maybe have a sales counter that would serve to show how many people didn't complain.