Bruce,
This one gives all sorts of possibilities for options. You could always be the top bidder on the chips and demand the chips back...but I wouldnt go that route.

I think if you send the seller an email through the "ask seller a question" option in the auction and point out that the check he sent you bounced. As well you can state that you expect Paypal payment for the chips this time, as you aren't willing to take another check from him. He definately has a Paypal account, because thats what he paid me with. Otherwise, you expect him to stop the auction and return the chips to you.

Obviously we can't assume that he had any malice in his not paying promptly or his check bouncing. He may just be one of those people that isnt able to stay on top of things. This may especially be the case if he has cancer and is dealing with craziness in his life. Not that that would be an excuse, but i think it may explain things. Non the less, the facts remain that he didnt pay in a reasonable time, (for many of us) and his check bounced.