No, you're not supposed to have him ship you the stuff, or anything else about the show, that's fine. Call it a done deal at this point, you have every right to. But really, this was nothing more than an inconvienence for you, and like I said before, you really don't have any money into it that you wouldn't have had in there anyways. People back out of things like this all the time. Is it an inconvienence? Sure it was, but you act like he ripped you off and owes you $750 when you haven't even done 3/4 of the things you and him supposedly agreed to on the phone. You now officially have put more time into this thread than you have lost in your and his transaction. I don't assume Dave is off the hook yet, since you did have his name on the flyers and the site, but realistically, do you think he owes you $750? Apparently you do.
This might be going out on a limb, but have you ever considered the fact that you might have benefitted from his name being on your flyer as much or more than he did by being on your website and some flyers? When Reptiles Magazine, Kingsnake.com, Zoo Med or any large company (and I tend to consider Reptster a large company) is put on a flyer, it gives THE SHOW SOME CREDIBILITY.
On top of all this, as was said before, you could have just waited on payment before listing him as a sponsor. Sure, we like to take people in the industry's word on things, but I think it should be just written down as a lesson learned. If you can get a few hundred bucks out of him for the flyers, more power to you.