Linking

My blog is non-profit. Its all about (plant profiles) For years I have been adding a buy it link to virtually any seller that has the item. Is this wrong regarding seo good practice. I ask this because if I go back a number of years every one of my newly published posts would be visible on the front page of Google search, often at the top. Now, and for quite a long time my new posts are hard to find in spite of my content and seo being much better.
Regards
Alistair

The page I need help with: [log in to see the link]