Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of used car seller CarMax (NYSE: KMX) were sputtering in intraday trading, losing as much as 10% after the company reported its third-quarter results.

So what: The numbers at CarMax actually looked darn good. Sales were up 23%, and comparable store sales showed an impressive 16% increase. Though earnings per share were reported as gaining just 9%, if you back out one-time adjustments in the company's finance division from the year-ago results, you get a much more robust 50% jump. The $0.36 in per-share earnings also waltzed past Wall Street estimates.

Now what: So what gives? Why the sinking shares? There are no two ways about it. CarMax is a pricey stock right now. For consumers pinched by the recession, buying a used car from CarMax may be a bargain, but with the stock trading at more than 20 times expected fiscal 2011 profit, there's nothing bargain-priced about it. I have no idea what investors might have been looking for this quarter to justify the price tag, but they obviously didn't get it. CarMax is a fine company, but investors may want to sit this one out until they can get a better price.

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Fool contributor Matt Koppenheffer does not own shares of any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or on his RSS feed. The Fool's disclosure policy assures you no Wookiees were harmed in the making of this article.