Rookie marketing mistake?

[mercphoto]

A new shifter kart track opened around here about 6 months ago. I know the owner and I offered to loan them some 16x20 prints in exchange for the exposure. They bought the frames and put them up. First race I got some sales, and did little marketing. Second race I did marketing and promotional work, but I was not the only guy photographing the race. I do only web-sales, this guy does on-site viewing and printing. So far I have zero sales from that race.

A) I'm assuming I can't compete with instant gratification.
B) I'm assuming I should have asked for exclusive commercial photo rights in exchange for the prints.
C) Should I ask to ammend our relationship?

Thanks.