This is entirely apocryphal, but my friends who are very into blind items and celebrity gossip tell me about “yacht girls.” Famous (but not too famous) women are often invited to rich guy’s yachts as soft escorts. Sometimes there’s sex, often they’re just there to be pretty and flattering. Apparently Zach Effron is frequently a yacht “girl.”

So yes, I think a fairly significant portion of minor celebrity income is from private appearances (of one kind or another). Speaking engagements for businesses or clubs are another big (legitimate) arm of this trade.