I've noticed that there's a few shops that are open on behalf of CHEs (Willow Hall is one such house which sells ranger rods and the like). I like the idea of shops being used in this way. It's a group effort and makes it easy to stock things.

I was just going to suggest that there is a partnership model where all partners are given rights to remove items and the account balance is grouped. This would allow players to jointly stock common magic items (say the CHE wants to stock wands, ruby amulets, etc). Just a few things that would be a lot easier: managing stock if players are away for long periods, stock consolidation and stacking, organization and re-pricing, pulling gear for give-aways, whatever. Also, the balance would be much easier to manage. Just less burden on one individual overall.

Maybe with syntax something like SHOP PARTNER (person) [GROUPED|DIVIDED] (or open/close or shared/personal)

I guess the easiest way to think of it is that there is a group (which the owner is always a part of) and they can invite partners as either members of the group or sole proprietors (who are independent). Or perhaps designate these rights on a per-room or per-container basis to allow more granularity?

From the armchair this seems the most possible and sufficient for the desires of the group shop model. Obviously a complex user/group system would be way more awesome but it seems more difficult (each partner can mark something for sale as their own, or make partnership groups where items are collective and sell them under a group name, funds are divided into group and individual accounts, etc).