Personally, I ask them get their own Wix account (unless they absolutely do not want to) .
When the site is done and they have completed payment, I will transfer the site, the premium plan, and the domain to them, I stay on as an admin or web designer (most keep me on as an admin though) .
You still get your points for transferred sites that you are connected to or had part in designing (maybe just double check in the points area on the partner dashboard before and after transferring) .