I usually read the negative reviews. If those negative reviews are for something that I can live with, that means I can discount half of them
For instance:
A sewing machine is panned badly because the automatic needle threader isn't. I can live with that. I've threaded needles all my life. Other things get bad reviews for adding another step to what some deem should be totally automatic.
It also means there could be good deals for those of us who don't mind a little extra work as long as the end result is really good.