Word of mouth is the most persuasive form of advertising. What would be more influential a giant ad promoting the national auto repair center or a friend who just got a great deal on his repairs at the local shop down the street? People go with recommendations because they are more trustworthy.
How does this relate to you? If you can tell customers about your own use of GuitarGames.net (truthfully, of course) then they are more likely to join, and you are more likely to make a commission. So try out the games, share them with your visitors, and watch your commissions grow!