I think Substack should NOT deposit the money until AFTER the refund period has lapsed. That way, the publisher can decide. If, in that first seven days, the new subscriber requests a refund, it can be given back without the publisher having to manage it in any way. I've had one direct request for a refund, which I granted- but I'd be pretty upset if money was deposited and then requests were made for $$ back on a regular basis.