My own search default with my store ID is price +postage, lowest first, and that's what my store items are now defaulted to if I view them (I previously had it set to ending soonest). I tried to change it in my shop settings, but it didna take.

I have it set to ending soonest on this ID, and my store items show as ending soonest when I check with this, so I'd say it's now (or at least temporarily) based on the buyer's search preferences.