Few companies are as easy to understand as media retailer Barnes & Noble (NYSE:BKS). True, competitors such as Amazon.com (NASDAQ:AMZN) and Overstock (NASDAQ:OSTK) are nipping away at sales and may well win the war for consumers' hearts. But Barnes & Noble offers a more attractive valuation, has also been online for some time, and is battle-tested.

Alas, all isn't as simple as it seems at the big-box bookseller. Looking at Barnes & Noble's most recent 10-K and proxy statement, I found some unexpected complexity due to the sheer volume of related-party transactions. On the bright side, many of the transactions are warehouse leases and shared services with barnesandnoble.com. Now that the online company is once again 100% owned by the parent, these should fade away (though, it does make me wonder how much the two can realize in synergies). However, a few of the other transactions raise an eyebrow.

Prepare yourselves, Fools, we're about to dive into the sordid world of related-party transactions. All the details needed to get an understanding of related-party transactions can be found in the proxy statement and the 10-K that are filed with the SEC. In both documents the section to look for is titled, "Certain Relationships and Related Transactions."

If you're unfamiliar with, or intimidated by proxy statements, you need not be. Fellow Fool Tim Beyers has done a great job explaining proxy statements here, and Chris Mallon followed up with an excellent piece here. Please note that while related-party transactions can be found in the proxy statement and the 10-K, the level of detail between the two documents can -- and as we'll soon see does -- vary. It pays to read both and do a quick comparison.

In its most recent 10-K filing, Barnes & Noble discloses a number of transactions between the company and entities controlled by Chairman Leonard Riggio and family members. But, the disclosures surrounding the airplane transactions are the most interesting.

For 2003, Barnes & Noble discloses in both its 10-K and proxy statement that the company paid for the use and maintenance of a plane that is owned by B&N College, a company controlled by Mr. Riggio. In addition, the company notes in both filings that B&N College sold a plane to Gamestop (NYSE:GME) -- which Barnes & Noble owns 64% of and controls 94% of the voting rights -- for $9.5 million.

In stark contrast, Gamestop mentions in its 10-K only that it purchased a plane from a company that is controlled by a member of the board of directors for $9.5 million, but makes no reference to the transaction in its proxy statement. Going forward, Gamestop shareholders may want to start reading the Barnes & Noble proxy statements. And shareholders of both companies should demand to know how much was saved by purchasing a plane from B&N College instead of flying conventionally.

At a minimum, investors should discount into any purchase of shares the effect of related-party transactions where one shareholder makes out better than the rest, because you never know what you might find in next year's filings.

If digging through SEC filings isn't for you, consider a subscription to Motley Fool Hidden Gems , where Tom Gardner culls through the universe of small-cap stocks for you.

Fool Contributor Nathan Parmelee does not own shares in any of the companies mentioned.