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The people who sell you mutual funds will tell you various things about them. They'll tell you about the fund company's great reputation. The fund's impressive "stars" and the awards it has earned. The terrific one-, three- or five-year track record.

Bah, humbug.

Here are five things you really want to know about a mutual fund before you invest -- but that nobody wants to tell you:

1. What are the fund's total fees, and where do they go?

You may think you know, but you probably don't know the whole story.

The adviser pushing the fund may get a commission. Sometimes, it's as high as 5.75%. There may be a charge if you sell the fund within a specified period of time. There are the annual fees -- the so-called expense ratio, which can vary from 0.1% of your money each year to 2%. These may include a 12b-1 fee, where you actually pay for the fund's marketing. And then there are all the costs the fund incurs buying and selling stocks. These are buried in a document, called the Statement of Additional Information, which the fund company does not have to give you unless you ask for it specifically. If a fund trades a lot, these costs will mount up.

The higher the fund's turnover, the worse it will be. A turnover rate of 100% means, in effect, the fund churns through its entire portfolio each year.

How much does all this matter? Fund companies typically do better than you do, just as Las Vegas casinos typically make out better than Las Vegas tourists.

Over 30 years, a fund with investments earning 7% a year, with no fees, would turn $10,000 into $81,500. A fund charging a 5.75% sales load, and 1.5% a year: just $49,500. That's barely half the profits.

Think about where the rest went.

2. Does the fund manager eat his own cooking?

A study by Morningstar a few years ago found that mutual funds tended to do better when the manager had a big chunk of his own wealth tied up in the fund, alongside yours.

Big surprise.

Now try finding out which ones do.

It's also buried in that Statement of Additional Information. Even this disclosure is new. And it's incomplete. The statement will not give you an exact figure for the manager's investment, only a range: A manager has no money in a fund, or has between $50,000 and $100,000, and so on.

And, critically, the statement will not tell you what share of the manager's wealth this investment is. Maybe a manager worth $30 million has $100,000 in his fund. So what?

Bottom line: Most fund managers have no money in their own funds. No kidding.

Warren Buffett is one of the richest men in the world, but he holds 99% of his wealth in his investment vehicle, Berkshire Hathaway (BRK.A, news), alongside the money of his investors. It shows.

3. Will the fund company put your interests before its own?

There is a conflict of interest between you and the company managing your mutual fund.

You make money if a mutual fund performs well. The fund manager makes money if the mutual fund gets really big. That's because the manager's main source of income is a slice of the assets under management.

Alas, the bigger the fund gets, the less likely it is to keep outperforming. Elephants don't dance.

As new money pours into a successful mutual fund, even the best managers find it harder and harder to make great investments. They struggle to find enough good opportunities for all that cash. They find they can no longer take significant stakes in smaller companies. And they can't sell out of bad positions so easily, either.

Investors do less well.

Meanwhile, the fund company takes in a management fee on greater and greater assets.