Partner Co-Marketing Lead Generation

A company selling a complementary, non-competing product to the same buyer already has an audience that trusts them. Co-marketing borrows access to that trust — through joint content, shared events, or an integration — in exchange for the same access to yours. Done well, it's one of the few lead sources that costs mostly time rather than money and compounds as the partnership matures.

Picking the right partner

Good fit      sells to the same buyer, solves an adjacent problem,
              isn't a competitive substitute, has a roughly
              comparable audience size (wildly mismatched sizes
              make the exchange feel one-sided)
Poor fit      technically adjacent but actually competes for the
              same budget line, or has an audience so much larger
              that the exchange is really just free promotion for
              you and negligible reach for them

"Solves an adjacent problem for the same buyer" is the test. A company selling expense-management software and a company selling corporate card products share a buyer and don't compete — a natural partner. Two companies both selling expense-management software, however different their features, are competitors regardless of how the conversation is framed.