What shopsystems do customers usually trust?

I have recently finished an ebook which I now plan to sell. So far I am going to use CreateSpace and plan to support Leanpub.com. Later I plan to publish more e-books.

In a few blog posts I read people are selling a lot ebooks directly from their websites too. While I could code something, it's most likely not as safe as many popular shopping systems out there.

When I told about my plans a friend, she responded to me that buying on some random website may not like a few users. When I looked at f. e. Shopify (just saying, currently comparing systems), it seems that you can almost hide everything which points to Shopify. It simply looks like it is a custom solution.

Now I need to find a balance between effort and best value.

Considering CreateSpace and Amazon as "set" because there are simply no other solutions, what kind of shops do customers usually trust and spend their money?

Is it better to go with a bigger distributor as Leanpub only and safe the bucks for Shopify, do I need both or is it better to just use a system like Shopify?

Sounds like you're over thinking this.

Given the question, I'll assume you're an author selling a ebook (could be wrong). Likely a single product, or a bundle of single purchase products.

Additional ebooks would likely require separate sites / messages / call to actions.

You're not a store with multiple sku's, inventory requirements and complex shipping rules. Shopify (and many other solutions) can be shoehorned into working for you, but likely is overkill in your situation.

If we are talking about increasing your market potential beyond your website, then leanpub / kindle direct publish / createspace (even packt or manning are options). Unless contractual obligations prohibit you from selling direct, these would be additional channels to get your ebook out there.