Every sale depends on three things happening at once, and each of those three things has its own evolutionary history, running for most of Earth's existence before a single human being was around to close a deal.
You have to be able to tell a stranger from someone you can trust - a problem cells were already solving with chemical self-recognition before there was a nervous system to do it with a handshake instead. You have to have something worth trading, and a way to move it - a problem solved first inside a single cell, moving molecules across its own membrane, long before there was a market to move goods through. And you have to have a way to make an agreement hold once you can't force it - a problem multicellular life solved by policing its own cells for cheating, long before anyone wrote the first contract.
Recognition, exchange, and the deal. Three different problems, three different timelines, three different sets of research - biology, chemistry, economics, anthropology, evolutionary psychology - that were never built to talk to each other. Enterprise sales is the place all three of them collide at once, in a single room, usually without anyone in the room realizing that's what just happened.
Each timeline below stands on its own. Hover any point for the detail behind it; drag to explore the full span, from the origin of the mechanism to where it shows up in a modern deal.