When you invest your hard-earned money through a broker, financial planner or financial advisor, do you really know who you’re hiring? Some of these professionals are legally bound to act in your best interest, while others may be out, first and foremost, to make a buck.

How can you tell the difference? Here’s what you need to know before you choose.

Start by asking one simple question

Ask the person you plan to work with, “Are you a registered investment advisor?” If so, that person is what’s known as a fiduciary — and thus is obligated by law to act in your interest before his own.

Every registered investment advisor (RIA) must file a form known as Form ADV. It explains in simple terms the advisor’s services, fees and approach to investing. It also discloses if the advisor has had problems in the past with either regulators or clients. Your advisor should provide this form on request. If he won’t show it to you, consider that a red flag. He should display it proudly, like a restaurant would display an excellent health inspection rating.

If you RIA doesn’t provide the form or you don’t want to ask for it, you can find it online, along with more information about his professional history. To know where to look it helps to know how much money the person manages.

RIAs are divided into those who manage more than or less than $100 million in client funds. The first group must register with the U.S. Securities and Exchange Commission. If your RIA falls into this group, you can read about him using a service called BrokerCheck. The service is from the Financial Industry Regulatory Agency (FINRA), a private regulator run by the investment industry. Another source is the SEC’s Investment Advisor Public Disclosure site.

The second group of RIAs must register with a state regulator. For researching these RIAs, start with BrokerCheck but also check the database of state-level regulators at the North American Securities Administrators Association.

Advisor, planner or broker?

A financial planner, broker or insurance agent who is not a fiduciary can be a perfectly good source of investment advice if you have a knowledgeable, scrupulous one — and you understand what his job is, and isn’t.

Brokers: These are salespeople. Their job is to purchase securities for you if you don’t want to buy them yourself. While they are licensed in most cases, the regulatory standard they must meet is lower than that of a fiduciary. The investments they recommend must be suitable to your situation, and that’s it. They aren’t obligated to act in your best financial interest. Some brokers call themselves “financial advisors” but aren’t in fact RIAs, so it pays to check. Note that some RIAs are also licensed to act as a broker.

Financial planners: These professionals can offer advice on investments but often focus on planning topics such as taxes, insurance and retirement rather than solely investing. They can’t purchase securities for you unless they’re also brokers. And again, unlike RIAs, they aren’t legally required to act in your best interest.

Insurance agents, tax planners and lawyers: These folks sometimes take on the role of financial advisor. Be sure to consider their advice in light of their licensing and experience. For instance, if an insurance agent tells you that an annuity is the best way to secure retirement income, get a second opinion from a fiduciary before taking action.

Greg writes about personal finance, business and technology. His work has appeared in Businessweek, Newsweek, Forbes, Bankrate and a variety of trade ​publications.