Prices can't go up forever. Just look at the housing bubble. Yesterday, Visa (NYSE: V) posted great numbers in a miserable economy and beat Wall Street's expectations. Naturally, the stock fell.

Visa's numbers would have been impressive in a good environment. In this market, they border on phenomenal. Profits jumped 28% to $314 million from $246 million, while revenue grew 22% to $1.45 billion year over year. In addition, adjusted earnings per share came in at $0.52 versus the Thomson Financial average analyst forecast of $0.46. And -- go figure -- the stock sold off nearly 6% in after-hours trading.

What's the problem?
Visa warned that domestic growth is likely to slow in the near future. U.S. business is still the biggest share of revenue and, although growth looks good so far this year, Chief Financial Officer Byron Pollitt warned, "At some point, the softening economy will likely impact our business in the U.S." Visa also issued three-year projections that many bullish prognosticators probably thought conservative.

So, what's the real problem?
While a slowing U.S. economy may speed-bump some of Visa's growth, the real problem is that the stock just got too darn expensive for anything but unbounded optimism. In March of this year, Visa went public at $44 per share with the largest U.S. IPO ever. Since then, the stock surged more than 70% to close Monday at $75.63.

Even if you believe Stifel Nicolaus analyst Chris Brendler's $2 per share earnings estimate for 2008, the stock is priced at about 38 times earnings -- a fat price in a lean market.

Visa has a phenomenal business for sure. Unlike other major credit card players -- such as American Express (NYSE: AXP), Bank of America (NYSE: BAC), Discover Financial (NYSE: DFS), and Capital One (NYSE: COF) -- Visa and MasterCard (NYSE: MA) don't lend money to consumers. Therefore, they don't share in the extensive and ever-escalating problem of consumer delinquencies. They just charge transaction fees and incessantly ring the register with their dominant market share of the worldwide trend away from cash to debit and credit cards.

What does this mean?
There's nothing wrong with Visa's numbers or projections. The problem is the stock price. It's awfully tough to post numbers good enough to boost the stock from 38 times earnings in a lousy market. As good as Visa's numbers are, they're still finite.

In this Fool's opinion, Visa is one of the best financial companies to own. But you have to get the right price, and this ain't it.

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Fool contributor Tom Hutchinson holds no financial position in any companies mentioned. The Motley Fool has a disclosure policy.