There are other issues here as well:

All quotes from the ekgaming.com Trade-In Page

First, we are only extending credit towards console games with a "new" retail value of at least $30. If a game's value drops below that you aren't going to get much credit and would be better off selling yourself online or on our sister auction site, http://www.GameGavel.com.
So in case we can't take your game, please sell it on our rival to eBay. An auction site where the publisher will not see a dime. EKG seems more like an extensive ad campaign for gamegavel rather than helping publishers.

Mail your used games to us today, get your new games in about 1 1/2 weeks.
Trading in games is usually about spur of the moment / instant gratification. Why would you go through the same process that selling it yourself takes and take a lower value since there's now a middle man involved?

3) Mail us your games along with a note displaying your Name, Phone # and Email Address. Mail your games to us using United States Postal Service 1st Class Mail (bubble envelope recommended). We will refund your shipping costs up to $3 per envelope for 1-2 games or up to $8 for boxed multiple games. We will add this refund to your credit amount.
As stated by someone else, I don't understand where the profit margin is coming in. If he's selling MW3 for $50 (just to use a number that's "cheaper than the competition"). That means the following:

a) He pays you $40 trade in credit for MW3 = - 40
b) He gives 10% Of the *SALE* to Activision = - 5
c) He refunds you the cost of shipping your game in = - 3

That means he's $48 in the hole before he sells the used game. A $2 profit remains, and that's before the overhead of any employee / supplies / rent / bills is factored in. If he's selling the game for $55 or so, then he's no better than the competition and it defeats the purpose.

Something is a amiss...