I met this young man went coming out Logos in Santa Cruz. He was carrying a couple of instrument cases and one case look like it could be holding a baritone. So I asked him about his instruments. It turned out that he was carrying a mandolin and a smaller guitar, as smaller instruments travel better.
I showed him my 1960's Favilla bari and he naturally started playing a little Sublime. He told me that he was the son of a violin maker in Idaho and that he's been enjoying travelling around. Then he played little snippets of several songs all by ear.
As he handed the bari back to me he said, "Now play one for me." As I hesitated, he said, "Just do it" in a very encouraging way. So I played Ring of Fire and after the first verse he joined in and sang along. I have really only memorized a handful of songs that I can play solidly from memory at a moment's notice. This reminds me of how I want to work on my musical ears.
Play Ukulele by Ear, is a site created by Jim D'Ville, that is all about using your ears. Jim also has a feature that he calls the 3-chord Club that he provides videos, sometimes tells you the actual chord, and then challenges you to hear where the changes occur.
So what was the lesson? Sing solid and strong. As the busker said just do it.