Citation? Ok, you asked for it...
"Instacart is infuriatingly bad. Replacing your main entree meat item with nothing, no call/notification, negates all convenience it offers"
"My 1st @Instacart experience will be my last. 26 of my 49 items have been replaced but mostly refunded so I still have to go to the store."
"i once had them tell a store had no cheese. completely out of cheese. no cheese was available to replace. i was naturally pretty cheesed off"
"@instacart Why should I continue to use you all if every time I order, a huge % of items are out of stock and replaced? Update your database"
"Same happened to me! 14 items, and 8 ended up being replaced. I'm going to give them another chance, hopefully it was just a bad shopper."
...and more.[1] Clearly the lack of integration with realtime inventory systems is a weak point. But perhaps you could clarify how the model is supposed to work.
[1] https://techcrunch.com/2017/10/01/instacart-needs-to-deeply-...