I would imagine to accomplish this, it would be a major feature change and Squarespace has no obvious place to make feature requests.
It could be solved by permitting REQUIRED addons that have vaulted credit cards, but I don’t see any way to make an addon enabled by default, it’s always buyer-optional.
It would be nice if I could set up a security deposit addon that is either automatically added to a customers cart, or MUST be added to proceed to purchase.
Someone at Acuity should have thought of this, it’s incredibly frustrating that this feature doesn’t exist.