Comment by cowlevel

You can also do adversarial interop. Whenever a restaurant signs up, go to them on doordash and have your intern key in all their data.

Heck, they don't even have to sign up. Just copy their listing from Doordash and when someone orders, place an order on Doordash if you can't fulfil it yourself. You'll probably need several phones to scale this, or you could make a doordash account per customer.

Once you have some drivers yourself, go around restaurants in your area and copy down their menus. Have drivers go and make takeaway orders.

Doordash undoubtedly used all these tactics. This is just how business works. Obviously doordash didn't order off doordash but they surely integrated restaurant ordering from places that already had their own delivery.

If you have VC funding, subsidize part of what doordash is charging so your prices are lower. IIRC Google did this once to the point where a pizza restaurant repeatedly ordered their own pizzas and made a profit, making front-page HN - don't go that crazy.