Have you collaborated on co-marketing with complementary businesses? How did you find partners?

One of my friends alex heiden is working on a power dialer rn and is planning on co-marketing via partnerships w listkit.io, smartlead.ai, and others. He was telling me he was able to get these partnerships solely on the basis that he did favors for the founders years prior to today without asking for things in return. Comes down to relationships id say!