Earlier quoted context omitted.
These services charge more for the items purchased than what you would expect if you were to purchase them at the store yourself. The $4 per delivery is simply a facade.
No, they don't. Google is quite clear that its prices for Google Shopping Express are the same as in store: https://support.google.com/shoppingexpress/answer/3423377?hl...
Some do:
Instacart: https://www.instacart.com/faq#inventory-and-prices-q2
Yes, Instacart prices are our own and vary from the store’s price.
Postmates https://postmates.com/help
Additionally, a 9% service fee is applied to the purchase price of your items.