I once bought a 1933 Excelsior from Goodwill for $110, then flipped it it for $350, thought I was pretty sly. Then the guy I sold it to (who worked for Campagnolo USA at the time) traded the bike for a Ferrari engine. Found out later I could have sold just the fenders off the Excelsior for $350. My ignorance, my fault.

This was before the internet, so info was harder to come by.

I kept my other '33 Excelsior, the one that I paid $10 for, which is my size. (The seller wanted $15 but I talked him down!) The one I flipped was in much better condition (almost mint) but too small for me.
Mine:

(Apologies for the photo from the left. I really should take a proper right-side pic!)