I just can’t find the information that shows me how, as an owner, I can invite clients as guests so that they only have access to one project file and don’t see all the projects our agency has. I am going around in circles in the documentation… 
Can someone here show me how to set this up?
Hello @Xhaust! 
I think the answer you are looking for is here!
You can invite people to documents by going to the “Share” menu, adding the person’s email address, and giving the person the desired permissions (View or Edit).
I hope I was able to help. Do let us know if you are still missing something! 
Thank you very much @Diegogdag , but no, that doesn’t help me.
If I do it this way, the invited person can see ALL our projects.
Nowhere in the documentation (at least not that I can find) is it explained how to set up guest accounts that only have access to one or more files that I have selected.
I tried for ages to set up a guest account a few weeks ago. I found it somewhere (without the documentation). But I don’t remember how I did it.
Furthermore (but this is not my main problem at the moment), it is not possible for me to see which projects the guests have access to in the “People” administration, although it is described in the documentation that this is possible. A corresponding menu item does not exist for me.
Hello again @Xhaust!
As stated here, “Unlike normal Workspace members, Guests will only be able to see the specific documents you share with them.” So, if you share a document with a Guest, such guest should be able to access just that document.
On the other hand, regarding the “permission directory”, I’m afraid that it’s a feature existing just for Business Plan Workspaces (more info here).
In any case, if you contact us at productsupport@sketch.com, we will be happy to check any information about your Workspace and its users! 
Hello @Diegogdag ,
but how exactly do I do that? That was my question all along.
I have just found out that I only need to click on SHARE within the document in SketchCloud and then enter the email address there so that the relevant person is automatically invited as a guest.
Yes, that is actually quite simple. But if the processes for inviting editors and viewers are quite different, as a user I assume that inviting guests is done in a similar way. And it was at this point that I got stuck…
Nowhere in the documentation did I find this explained so simply. Either I am too stupid or it is not sufficiently described in the documentation.
In either case, this might be interesting feedback for your considerations.
Thank you for your patience.