Congratulations on make a profit on 7search, most folks on this forum reported trying that network failed to make a penny. I’m sure there are some things you are doing differently from the pack, besides the focus on extremely relevant keywords.
There is no need to limit it to only a few keywords per offer unless those are the only extremely relevant keywords you could find. All extremely relevant keywords should be tested. Just make sure you follow the advice of sticking with the most relevant and specific keywords you can find.
My advice for people doing direct link affiliate marketing is to target branded search terms, those are most often used by people who are about to make a purchase and it is generally the best way to achieve profitability in ad campaigns for affiliate offers. You are riding the coattails of everyone else’s marketing efforts without spending any money until the last click of the search funnel. In affiliate marketing, the only one paid is the last click affiliate, so it’s crucial to focus your ad spend exclusively on “last click” keywords.