The founder would then send out a mail to the addresses in Pile A saying "pay us $25k and we'll forward your details to Pile B using our Top Secret Algorithm". No computers necessary. And genius.
"Hey YC companies hit me up, I'll order all the sandwiches this Thursday.
"Hello Bay Area restaurant, I want to place a $4k order this Thursday and every two weeks for the next six months. Can I talk to your owner? We have some requirements to make this work."
"Hey Valley IT company, tell me your dietary restrictions and food magically appears at your office, for the low low price of [guesstimate: $400 / employee / month]."
"Hey Valley restaurant, we're really loving the sandwiches. Here's an order for $6,000 and please pay extra special attention to the note about the vegan ones. I know it's a hassle but then again I do order $6,000 of sandwiches at a time so I expect you to deal."
In the process you'll discover things about this process which suck, and you can automate or systemize them as business needs/opportunities dictate.
The example from the book that comes to mind (and I forget the name of the startup) was a grocery delivery app. They started out by manually going up to people at the grocery store and offering to give them suggestions on groceries to buy based on meal ideas. Eventually, they got someone to agree to participate and provided enough value to the person that they could - and did - get paid by the customer. This helped validate their idea to started building out the app that would do the same thing using software.
They have a feedback form that's emailed out an hour after lunch, but the actual suggestions we provide go largely ignored. Several employees have described it as them having really short-term memory.
They also seem to insist on "trying out" restaurants again that the entire company dislikes.
Further, the feedback (when taken into account) never seems to apply to the company, only to the specific restaurant. For example: we request that next time $sandwich_shop delivers to leave the bread dry and put mayo and mustard on the side. That happens the next time $sandwich_shop delivers (though frequently not the time after that), but does not happen when $other_sandwich_shop brings food.