Have you actually managed ecomm campaigns where you've done this? If so, how were your tags set up to facilitate this, particularly solving for the obvious cross device challenge?

I'm genuinely curious because those of us that are experienced in the hands on management of this stuff know how hard of a problem that can be in some circumstances.

Fwiw exclusion lists can be very effective if you can properly cookie someone at the appropriate time or leverage a data broker to pipe in CRM data. But it is by no means an easy thing to solve for.