You win... with a great effort!

Using all of your force. Going all out against him. The two of you arm-wrestle until sweat, and veins bulge. It's only by the end of a laborious minute that your hand slams his down, securing your victory. Despite his valiant attempt at victory, owing in part to the promised reward, he lost anyway. Then again, such was life. And so was the prospect of your victory... What reward would you want for such a feat?