Odds of Getting In
As with most jobs that require few qualifications, allow you to work for yourself, and have a somewhat unlimited earning potential, there are going to be a lot of people interested in getting involved. Some of your competition will take it seriously, others will sully the job title so much that you'll be tempted to pretend you have a different job when strangers ask what you do for a living.
Most people with whom you interact aren't going to know the difference between the good and the bad, so to succeed, you're going to need to know your stuff and prove your worth.
There are, of course, different ways of doing this but most involve landing a few clients, and doing a really, really good job with them, thus growing your network through word of mouth. Do that, and you've got a good shot at getting into (and staying in) the brokering game.