Anything like that, or ask for an upgrade and the CMs use points to do so, etc.
Yep, you will be liable, and Disney will bill you.
If you rent your points out through a Broker then they would presumably go after the owner for the costs, but Disney will still expect you to pay the damages. If you rent the points out privately, I don’t know how you proceed.
The upgrade situation is the one that worries me, simply because it does happen from time to time. CMs will sometimes just borrow points to do so. Even through a broker it could still affect future plans. For example, we bank and borrow to visit every 3 years. We have just under a hundred points just now that I will rent out. If the renter was to use an extra 50 points, that would affect our plans for the next stay.
Personally that’s why I will use David’s to rent my points.