I think, from the venue's point of view, it has more got to do with the maxim of getting something as cheap as possible.

Agents and venue owners can spot the over-compromising artist, and some are ruthless enough to take advantage.
I wouldn't call it 'stealing gigs', though.

One should have confidence enough in one's own capabilities before one steps on to a stage. Musicians are not born publicists, but ultimately it is down to the individual's engagement in what they do, to further themselves.

B.