I am trying to find a niche for my semiauthority site (plan to do 100+ posts). Thus far I found one that has a lot of amazon, ebay, walmart and such type of sites on the first page. They all have usually pretty low PR 0-1, some occasional higher PR, very often they have zero to couple of backlinks (according to Market Samurai) and very little on-page optimization (a lot of them don't have the kw in title and url). Only thing that seems to be working for them is that they are Amazon, Ebay, Walmart and they have very old domains. Should I go for the niche or should I keep away because Amazon, Ebay and Walmart will outrank me?