Never Let the Two Sides Shake Hands Without You.

The single greatest fear of every middleman, and the thing that kills more of them than competition ever will: the buyer and the supplier meet directly, look at each other, and quietly cut you out. It's called disintermediation, and it has ended a thousand fortunes. If your only value was the introduction, then the introduction is the rope they hang you with.

So you never rely on the handshake. You make yourself the thing that has to stay in the room - the guarantee, the quality control, the single point of contact, the brand they actually trust. Build it so that even when both sides know each other perfectly well, going around you would make the deal worse, not cheaper.