Is it possible to have a setting where a contact can only be in one list?
I collect leads via FB ads and they go into a marketing list and when someone signs up via my business software they go into my members list…but often contacts end up being in both lists…
I would probably solve this by setting up automations for any form submissions. Then you can easily add a step where you either unsubscribe from all lists (but make sure to put that before the step where they subscribe to the list you want them to be in), or set up unsubscribe-steps for each list individually (unsubscribe from list 1, unsubscribe from list 2 and so on).
Maybe there’s a setting that would eliminate this as a problem, but as a solution it really isn’t that complicated