I imagine that a truly top-notch virtual assistant would always be listening and aware of your behavior and context. However, the level of trust required for such monitoring is usually reserved only for one or two people in our lives, and even then, it's quite incomplete awareness on their part.
I don't know how a for-profit company can reconcile this disconnect, though I imagine that someone will eventually try.
Instead, you could go easy, by first suggestint the user to set up your assistant by linking it to amazon, deliveroo/uber eats/etc, facebook, and verbally sharing information as it asks. Then, over time, it could spread its inference further and further and you won't be sure or not if you already shared that information or not, but you will just assume you did, as you share everything anyway. For people who are not so open, it could stick to inferring less and being less useful.
The issue is of course, like paying for youtube, is consumers will wonder why they would want to pay for an assistant.
This is a complicated social construct even with people. If a public relations person (or whoever in a professional context) reaches out to me, I hope they've done some basic research on what my interests are. I saw you were at $CONFERENCE last month? Sure, probably. Start asking me about my vacation last month that they found photos from on Flickr? Probably getting over a line if I don't know them.