(MONEY Magazine) – Under extreme pressure to meet their commission goals, stockbrokers don't always do what's best for their clients. That, at least, is the view of Mark Dempsey, 33, who spent almost three years selling stocks and bonds for one of Wall Street's biggest full-service brokerage firms until June 1995, when he was let go for refusing to meet sales goals he called unfair. Today he runs a financial consulting business in Dallas, advising investors about how to manage their accounts and protect their interests. Below, Dempsey describes the most common mistakes investors make in dealing with their broker:

Here's the most important investing tip you'll ever receive: Don't trust your broker 100%. I say that with insider knowledge, because for nearly three years I was a successful broker in Dallas. Within my first two years, my bosses expected me to amass $10 million in assets, open 150 accounts and generate $150,000 in commissions. I did just that. How? By becoming a supersalesman rather than a first-rate investment adviser.

One thing I learned: While I couldn't rely on the market to go up or down, I could always rely on my clients to make the same mistakes over and over. Now that I'm out of the business, I'm free to tell you four ways you can come out on top when dealing with your broker, as well as two things you should do when choosing a new one:

WHEN DEALING WITH YOUR BROKER

--Always ask for a discount. Repeat after me: You can get price breaks on your stock trades. At my firm, I could discount up to 35% without management approval and waive certain customer account fees altogether. This kind of flexibility is common at full-service brokerages. But you might never know about it. When clients balked about their fees, I would generally tell them that you get what you pay for. Not true! Always ask your broker for a discount, and think big: Ask for 50% off the stated commission and then negotiate a compromise.

--Demand that your broker pay attention to your account. One day at a monthly sales meeting, a fellow broker asked how we manage our smaller accounts. The sales manager stood up and gave the correct answer: 'We don't.' To commission-hungry brokers, bigger portfolios are almost always better. So if your portfolio is chickenfeed compared with your broker's other accounts, you could get hurt. Here's the corollary: Brokers focus more attention on clients who demand it than they do on clients who don't. The lesson? If you're not a big wheel, be a squeaky one.

--Ask your broker about the cutoff date for meeting his commission goals. Most firms pay their brokers once a month, based on how much they've generated in commissions. As the cutoff date for meeting commission goals approaches, commission-motivated trading increases. A new study by two professors at Western Washington University and one at the University of Florida-Gainesville, who scrutinized the trading records of 100 Wall Street brokers from 1990-92, revealed that 29 consistently earned a 'significantly higher' portion of their commission income during the last full week of the month. Seven earned 40% or more of their commissions in the last full week of the month. Be wary of recommendations your broker makes to you at this time.

--When deciding how much to buy, let your comfort level be your guide. My office manager was fond of the 'Ask till they gasp' maneuver. A broker would propose that a client buy so many shares of stock that he'd gasp; then the broker would back off with a recommendation for a slightly lower number of shares. This technique lets a broker quickly learn your tolerance level, so he can sell you as much as possible. Always let your own comfort level and investment needs--not your broker's commission goals--determine how many shares of stock you buy.

WHEN CHOOSING A BROKER

--Pick a broker based on your own research--not just because your C.P.A. or lawyer says he's good. Such pros represent a broker's biggest source of referrals, yet they often know very little about the broker they're recommending. One C.P.A. referred his clients to me after knowing me for only two days. In another case, a local attorney talked me up to his clients shortly after I promised to pass on some of my clients to him.

Before doing business with a broker, always visit him at his office so you can form your own impressions, and check him out thoroughly for complaints filed by other clients. Also, be sure to ask your broker for evidence in writing of his professional credentials. [For a helpful number to call to do a background check, see page 21.]

--Say no to cold callers. I spent hundreds of dollars on lists of prospects whom I cold-called with a 'special' offer. My offer was rarely special, and accepting it was always a bad idea, for the same reason it's a bad idea to listen to a psychiatrist on the radio: The advice is given without knowing you.

To reduce the number of unsolicited calls you get, when a broker phones, tell him to put your name on the firm's do-not-call list. Then send the request in writing to the broker's compliance manager to make sure that it's honored. Rushing into a broker's arms, sight unseen, could be the ultimate bad blind date.