What is the difference between a broker and a RIA?

At the most basic level, a broker is a salesperson and a distribution source, while an RIA's and the IAR's that work for the are professional service providers. That said, the lines can be blurred to the point it's not clear which structure provides the best source of information, access and advice. This is why it's so important to understand the operational landscape governing financial services.

Dear Steven,
I suspect you know the answer, but here goes. A broker is essentially anyone who sells investment products. A Registered Investment Adviser must meet established standards to achieve that title. Those standards vary from state to state. The most important issue, I believe, is the issue of fiduciary responsibility. Fiduciary responsibility means that a financial adviser must put the interests of his investors first above all other factors. A "broker" may be selling products which provide the broker a financial benefit. That constitutes a conflict of interest, because the broker has to balance his own financial gain against the interests of his client. So, I recommend you find an independent financial adviser who charges a fee for service and doesn't make money on the sale of investment products, and who adheres to the fiduciary standard.
Best Regards,
Hugh

There are numerous differences, not the least of which is the legal standard they are held to concerning client service. Other differences are incentive and payment structures, product access, training requirements, disclosure requirements, and many many others.