Are shoppers allowed to turn down orders?

This shopper kept saying larger items were not on stock - it seemed like they just didn't want to deal with it, the store said it was clearly in stock.

One of the items was a 24 pack of Gatorade, when they said it was out I added 4 6 packs and I got this message asking me not to add anything to the cart because they were doing 2 other orders and the shopping cart is too small.

Seems like it's just not my problem and sucks they are kinda lying about it but a part of me feels for them also, what's the best solution in situations like this?