More airport stores could mean higher sales for retailers. One retailer who's already taking advantage of this opportunity is bagel seller Einstein Noah Restaurant Group (UNKNOWN:BAGL.DL), but this company might not be the best way to invest in this market. On the other hand, high-end cosmetics and clothing companies could find this to be a great way to gain some more customers.

The bagel shop sees potential for higher volume
An important metric declined this quarter for Einstein Noah, but the bagel shop may have another way to boost revenue. Comparable-store sales dropped 1.4% even though the average customer spent more money at its restaurants. This performance wasn't very impressive, but the bagel shop still managed overall sales growth of 0.9%, assisted by a much stronger gain of 11.7% in franchise and licensing revenue.

Einstein Noah does plan to add more restaurants, but with comparable-store sales falling, this might not result in impressive revenue growth. This is where airport sales could come into play. According to Einstein Noah, "our licensed partners are adding more high-volume airport stores in 2013 than they have ever done before." Busy bagel shops at the airport could definitely help Einstein Noah improve its overall revenue.

The appeal of airline travelers
Airline travelers offer a great opportunity for retailers. People who are waiting for their airplane to arrive can't shop at stores outside the terminal while they wait. Waiting for a plane is very boring, so travelers might buy products just to pass the time. Also, the travelers inside the terminal can afford to buy airline tickets, so they have at least some money to spend. This is even more true for travelers on costlier international flights.

As you might expect, the stores that manage to get spots inside the terminal can deliver great results. High-end retail stores inside airports can achieve higher sales per square foot than even high-end retail stores in prime downtown locations. This metric is very important to consider, along with comparable-store sales, if you are considering an investment in a consumer goods company.

Airports have also noticed this opportunity, since high-end retail stores can also mean additional revenue for airports themeselves. Instead of paying fixed rental rates, retailers inside the terminal typically have to pay additional rent to the airport when their stores achieve certain sales thresholds. Airports in the United States have been signing up more high-end retailers recently, as well as increasing the space they have available for merchants.

Stocks to consider
A wide variety of companies that sell food, clothing, and other consumer products appear in airline terminals. The companies best suited to benefit from this trend make a significant amount of their sales at the airport. Back in 2011, the Fool's Amanda Buchanan pointed out this trend, and she recommended cosmetics maker Estee Lauder (NYSE:EL) and the handbag maker Coach (NYSE:TPR) as companies that could benefit from growth in duty-free sales at the airport.

Estee Lauder recently reported results for its first fiscal quarter of 2014, which show that duty-free shops at the airport are still paying off, especially internationally. The company's Europe, Middle East, and Africa segment reported 8% sales growth, with the explanation that "The net sales increase was led by high-single-digit growth in the Company's travel retail business and double-digit growth in the United Kingdom and Switzerland." This segment did report 8% lower operating income for the quarter, but Estee Lauder explained that this occurred because of investments and expansion costs. Estee Lauder also narrowed its 2014 earnings per share guidance from $2.74-$2.87 last quarter to $2.80-$2.87, another positive sign. 

Duty-free shops could also pay off for Coach, but this company hasn't been doing as well recently. Although the handbag company did report 35% sales growth in China, its total international sales growth was basically flat at $365 million, compared to $367 million in the first quarter of fiscal 2013. The company has recruited the designer Stuart Vevers to help turn itself around.

On the other hand, Coach's competitor Michael Kors (NYSE:CPRI) has been on fire. Since Coach and Michael Kors both compete for some of the same customers, an investment thesis that works with Coach's business model could also apply to Michael Kors. Both of these retailers recently added stores in New York's JFK airport. Michael Kors also recently added a store in the Los Angeles International airport. 

My Foolish conclusion
Retailers have provided evidence that duty-free shops at the airport can lead to better financial results. This is especially true for high-end retailers because of the demographic that shops at these stores. However, this trend isn't strong enough to make up for other weaknesses such as declining comparable-store sales. Companies that are already doing well, such as Michael Kors, offer better opportunities to take advantage of this trend.