For me this is a question to avoid buying licenses.

You can make a temporary account for your customer in a group and share this with this customer.

If your customer desires to have its own space, he/she needs to buy its own workspace and you work within that workspace. I can in such a situation that you have a shared interface in tixio.io to share over workspaces the documentation/wiki data.

In the end the guest customer data will be published publicly or within your space as a group or in its own workspace.

The second question derived from this question, how can i make a closed wiki published for a larger public, but not for everyone to see and open.

We're glad you suggested it as well. It's now under our plan and soon be staring the work on it. You'll keep receiving our progress updates here.