A bunch of friends designed an app for small businesses. They asked a local macaron store manager to test it. It didn't fit her needs because her only need was to be able to deliver food to the customers. Their app was buggy and had some useless features. Also, no restaurant offered food deliveries in Palo Alto at that time.
The guys interviewed about 200 local stores and restaurants, and the feedback was all the same: problems with deliveries. So, they then tweaked their idea for the startup and set up a page PaloAltoDelivery.com to fill the niche. They focused only on food delivery. Their page had PDF menus copied from various restaurants and the creators' personal phone numbers. But, they first tested the demand among students.
They printed out some flyers and put them around the Stanford University campus. They changed their name to DoorDash after a few months.
They charged $6 for delivery. They were students and food delivery drivers at the same time. They succeeded because they had their own drivers, while other, similar apps only boosted restaurants' sales.