I'm not entirely sure what that implies. It's in the consumer's best interest to check reviews of products when selecting something to buy. How else would you wade through competing options?
Furthermore, 4chan has no search feature so I don't know how that's even equivalent.
Depends on the product. For Game Reviews, Steam reviews are better.
The problem with reddit is that just because someone recommends a product, doesn't mean they actually bought/experienced it. That being said it is a great way to find a product's defects, as people usually post to reddit.
If you need to actively find a review for some item you want to buy it's probably not that great of an item imho.