Ideally, you are someone who has owned his own business and knows what it is all about. You know how to read P&Ls and Balance Sheets. You understand lending and Cash Flow. In some states, you will need a Real Estate License, but even if not required, you should have one; many businesses include Real Estate as part of the deal.
The IBBA is the professional organization that provides formal education, but sadly, most Brokers have no such training. I would start with the IBBA and the most well regarded Brokerage you can find, in your area.
Most successful Brokers are retired from business or banking. They live off of their retirement, until they get to a break even point. I don't know what the current statistics are, but historically, it was said that it takes the average Broker three (3) years to break even on monthly expenses. Because some people think commission rates are relatively high, confidentiality makes each listing a process of intense, personal communications, rather than mass advertising. This is a very time consuming process and any Broker that lists a large number of businesses is not doing any individual Seller any good. Although some Brokers make a lot of money, it is definitely not a "get rich quick" opportunity.

Web reference: www.bafgroup.com