You can assign the license to any project, also those that you don't own:
http://www.concrete5.org/documentation/how-tos/designers/add-licens...

So you just need to belong to that project for the time you transfer the license there. You could also create a separate project, assign the license there and then transfer the whole project to a new owner:
http://www.concrete5.org/documentation/how-tos/editors/transfer-a-p...

If you want to transfer some money on those transactions, I think it is also allowed because in the license terms I don't see anything that would deny this. It only talks about the assigning of the license and I would guess it's ok because you just act as a "retailer" for that add-on in that situation.

But if you want to transfer money on that license transaction, I think that this is something you need to handle on your own.

We also have 0-usage for the add-ons we've won, I only touched one of them because one of my clients had that add-on installed and asked some advice with it. I just leave them "lying around" there in case I need them on some project.


Antti / Mainio