Who says you can't get decent investment ideas from the obvious places?

This morning, I noticed an interesting story in the Wall Street Journal that described the complaints of various airlines serving Latin American markets. These airlines are being pinched by many factors, including the usual: competition and volatile fuel prices. But in this case, the Latin American Air Transport Association (ALTA) singled out certain Latin American airports, claiming they are charging too much for fees.

It made me think we should create an investment rule of thumb, something along the lines of, "Follow the complaints to cash."

For U.S. investors, the obvious endpoint is in Mexico, where there are now three airport operators trading publicly, including GrupoAeroportuario del Sureste, known by the acronym ASUR (NYSE:ASR); GrupoAeroportuario del Pacifico (NYSE:PAC), which we'll call GAP; and newly IPOed GrupoAeroportuario del Centro Norte (NASDAQ:OMAB).

But as an investor, what do you make of it? Do you marvel at a business that commands a monopoly and exhibits fantastic scalability (during the good times)? Or do you run for the hills, expecting high-level complaints to bring future government clampdowns?

I stick with the former; I don't think there's much to worry about. In the case of ASUR, the major proportion of revenues comes from fees on more lucrative international travel, mostly at vacation hotspot Cancun -- coincidentally, the location of the ALTA meeting that brought about these complaints.

Here's the reality: these tariffs are already highly regulated by the government. Anyone really think a recently elected, reasonably conservative Mexican government is going to suddenly take it easy on free-spending foreigners arriving for a holiday? Yeah, me neither. And investors in this, or Mexico's other publicly traded airport groups, should keep in mind that tariffs and related, government-regulated fees aren't the only way to drum up business. There's further growth potential for licensing food and other airport conveniences.

In other words, I don't think grousing from the airline operators is going to bring them any relief on fees, and even if it did, I wouldn't expect much of a dent on airport revenues.

In fact, the monopoly position and steady cash flows at ASUR and GAP are prime reasons I'd rather hold these companies than just about anything else in the travel space. Let Expedia.com (NASDAQ:EXPE) and Priceline fight it out. Let AMR (NYSE:AMR), Southwest (NYSE:LUV), Continental (NYSE:CAL) and the rest of them have their price wars.

The airports won't feel the pain of those self-inflicted wounds.

GAP and ASUR have both been market-beating recommendations from Bill Mann and Seth Jayson. Bill leads Seth and the rest of the team at the Fool's newest premium investment service, Motley Fool Global Gains. If you'd like to get in early on a world of investment opportunities, a free 30-day ticket is just a click away.

At the time of publication, Seth Jayson had shares of ASUR, but no positions in any other company mentioned. View his stock holdings and Fool profile here. GAP is a Motley Fool Hidden Gems pick. Priceline is a Motley Fool Stock Advisor recommendation. Fool rules are here.