[gramontblanc]

Substitutions are omnipresent in my experience, but I view that as a symptom of almost all stores having really profoundly bad inventory tracking (do the developers for the web platform even know whether they have any items on the shelf at all?) so even with ordinary infrastructure hiccups I'd expect there to never be completely filled orders.

I don't know too much about the way the restocking priorities are established, but it appears to be totally ad hoc and at the behest of the shift worker on the line at the moment your order us started from what I've seen. The stores would need to have inventory systems fine grained enough to know that there are high margin items in stock to be swapped in to implement this kind of malicious action plan, but I think most stores (that aren't Walmart) don't even have their inventory spatially mapped at all, let alone multiple times per day to actively dump target items.