Late in the thread but here are my thoughts:
1. Check product availability date: If it's just launched and has too many reviews, either it's great item like iPhone or really a good deal/promotion or reviews are fake.
2. Check reviews: One or two liners that just mention, work good, great thanks are probably fake.
3. Check reviewer:
New user along with 1 and 2 above, fake.
Ignore reviews by 'Top 100 reviewer' or high volume reviewer as they get tons of items for reviews due to their status and don't have enough time to properly test anything except whether the item works or not. Some items may work that way fine but most need more details.
Check other reviews of the reviewer and if everything has 5 stars and not enough details, most probably they were free for review so biased even though first line of the review says unbiased.
So look for reviews from who's not new, not a high volume reviewer and has details on the item instead of one/two lines.
4. Reviews with pictures/videos at least suggests that the reviewer has product in hand.
5. Reviews with comments and follow ups provide more info.
etc...
Amazon reviews are trustworthy if you can filter out the junk.
Amazon has that side bar to filter products with '4 starts and above', '3 starts and above' etc... and kinda force new product to buy reviews otherwise they don't even show up in the page.