I would prefer "no markup, no tip and a single, and a higher delivery fee" - but offering "no markup" on grocery items (without direct access to inventory systems) is probably hard, since prices change so frequently.
In theory, you could market it as a fixed price delivery like Postmates does for some stores, and not show actual prices on the items, just say they will be delivered "at cost" along with a receipt. A challenge with doing this is charging someone who orders 75 items more than someone who orders 10 items.
It would indeed be very hard to do this without charging a markup if you want to show customers the price in the app before they buy. This seems like a pretty important feature.
On the other hand, the challenge with a higher delivery fee (say $10/delivery) with no markup is that a competitor could simply charge a higher but opaque markup, and a lower delivery fee (say $3.99/delivery) and appear to be "cheaper". The only way you'd find out for sure is by comparing item by item between the two competitors - which most people are loathe to do.
