Creating and selling templates

I’m progessing slowly with web design having build a few sites now but I’m thinking of designing some templates that can just be sold ( without customising )

How is this done? Say i want to sell a listing template and shop template on ebay?
Is there software that can be provided such as wysiwyg software for the customer to edit easily?
Are there any tutorials for this kund of stuff?
Where to start?

Some sites with an existing customer base allow you to build themes like Weebly or Shopify and then sell them through their theme store. Or you could build themes for Wordpress and sell them. That’s what I would recommend - building templates for a CMS that is already popular rather than trying to build your own.

You can just design the templates in Photoshop and sell the PSD file. Just make the listing on your auction site and bidders can buy it once it reaches the right price.
When you sell the PSD only, they will need to hire a coder to make it usable.

Building wordpress design themes is definitely more worthwhile. They will be easier to find from platforms selling themes and their use is much more widespread.