Acorn4, your post brings back some very -- fond? -- well, let's say "vivid" memories of open mics back in the day!

And - while I don't know if this still goes on a lot these days - back in Greenwich Village, at Gerde's Folk City, back in '63, my first experience with open mics (called "hootenannys" back then) was this:
I signed up early and was scheduled to go on about 10:30 PM. Then all the "names" (the Tom Paxtons and others who were doing paid gigs at the bigger name, cover-charge+minimum clubs in the Village) kept coming over on their breaks and cutting in line, so to speak, eventually bumping me back to about 1:30 AM -- by which time I had had 5 gin and tonics and could scarely keep track of my lyrics, much less my chords, but the audience was in the same state so they seemed quite contented with my gawdawful performance, to the point where the experience actually BOOSTED my confidence enough to allow me to do a stone-cold sober performance at another "hootenany" at another club the following week.   The point of this story being that, yes, the "pros" and up-and-comers do (or at least did) use the open mics for promo and publicity for getting more paid gigs.