Thanks Cam, after sitting back and having an honest think about it the answer is no. The ebooks I have are widely in use and as such I would be competing against much more established competition for a share.
I think I was hoping this was something i could set up and leave to run but I think the running costs would outweigh any returns unless I literally pumped money into it.
I have been looking into long tail keywords to find a niche using a handy guide on shopify. I have a keyword phrase BUY *** ******* **** which i like when I run it through keyword planner with only close related results I get no other keywords.
If I run it through google using the MOZ toolbar the top result has a PA of 45 and DA of 91 Ebay
Looking at the first 3 pages of results the highest PA is 47 but with a tiny DA
The highest DA is 91 but with a PA of 13.
Now I am still reading up on things but would you say it sounds reasonable that with a good site and SEO I could attract customers ?