I look only at the negative reviews. You can trust them to highlight the weak points of a product. So I know at least what would be the "worst" case scenario and if that works for me I buy it.
I prefer to 2 to 4 star reviews. Too many of the 1 star reviews are people who received a defective product or had other unique issues that I'm unlikely to encounter.
When buying a product I look for the reviews about it breaking. Once I know all the common ways the product might break I have a bit of an idea how long it will last. I can then also look up how much the replacement parts for the most likely to break parts cost as well as how hard they are to replace.
In my experience a lot of products have a single design flaw that causes almost all of the breakages excluding drops/water damage. I had a set of skullcandy headphones that the little arm thing on the ear part would snap just from the force of putting them on and taking them off too many times. Got a replacement and it happened again. Checked reddit and saw everyone has this same problem. Ended up getting the store to exchange them for a different pair.
This is something I do too. Recently, I stumbled upon a product where this was exploited. It read something like that: "Are you like me and read the negative reviews first? If that is the case I have to tell you that this product is really great!..."
My approach is to only look at the reviews with photos. That's usually a good way to find high-quality, detailed reviews. Just click in the customer photos section and you can scroll through the reviews.
This is purely anecdotal, but I've noticed recently a trend of reviews that start with "I was sent this product for free in exchange for an honest review..." and they almost always include photos. True, these are easy enough to skim over, but people planting fake reviews could also be getting smarter and making their reviews seem real by including pictures.
They're not necessarily fake, but they may be incentivised. I've had offers of a £5 voucher for a photo review or £10 for a video (the product was a £15 solar panel). No idea what happens if you slate the product, but amazon would probably refund you if it was that bad.
Sellers are well aware how much of a boost a photo or video from a verified purchase can give.