I think I would ask him how the bow is shooting for him. I know that I haven't had my bow out since the end of the season. I just needed to not shoot for a little bit.
If he has it, but hasn't found the time to shoot it enough to see if it is a good fit, then maybe invite him over for a evening of target practice.
I think there are ways to find out what he thinks of the bow. If he says he's been shooting and it is a great shooting bow. Then you can bring the 100 dollars up. Just a way to ease into the conversation.
If he doesn't like it, say you might sell it on Ebay.