My rule of thumb is that 1 star reviews on Amazon have to be more than about 7 or 8% before they warrant much credence. Below that, I have found that the negative reviews are usually from people who didn't read the description, have wrong expectations about the product or are complaining about the delivery or other things that are not relevant to the product itself. I would even discount the one review cited above unless many people complain about it because he might not have cleaned off the shipping grease from the new hammer. Who knows? I may still scan through the 1 and 2 star reviews looking for a recurring theme but usually it is just the idiots who can't read and 7-8% seems to be the tipping point where real issues show up in the negative reviews. Of course unless it is a recognizable named brand item, if there fewer than about 300 reviews (1000+ would be better) you are taking a risk regardless of the reviews because the product probably has not been around long enough to fail for people. Some sellers create a new listing when the reviews trend badly to hide the fact that it is a crappy product.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.