While I'm no lawyer, I believe your seller was contractually bound to sell you the item in question at your agreed upon price. (As I recall, an enforceable verbal agreement/oral contract exists when there was an offer, an acceptance of the offer, and a consideration of value exchanged; your agreement appears to satisfy all three tests).
Thus, if you really want to get the item you agreed to buy -- at the price you agreed to pay -- you could file a small claims action against the seller to seek specific performance of his contractual agreement to sell it to you. You wouldn't need a lawyer to file such a suit. However, you would probably need to file the action in the seller's home state & county which might be difficult for you if he lives far away. Also, different states have different limits on how much can be sought under a small claims action (these range from $1200 to $5000 or more), so you would need to check the limits in the (non)seller's state to be sure the amount you would claim (i.e., the amount you agreed to pay) falls within the allowable claim limit. Perhaps one of the lawyer/audiophiles who visit this site can give you better information about your legal options.
This said, I think filing suit should be a last resort. If you still want the item you sent payment for, you should start by telling the guy you want him to honor his original agreement to sell it to you at your agreed upon price. It may not too late for him to get out of the other deal; and even if he already sold it to the other buyer, he might still be able to get it back since that other buyer was apparently from his local area. If the seller refuses to honor his agreement with you -- and you're sure you don't want to pursue legal action -- then you should, at the very least, ask him to refund you for your postage cost and M.O. fee. (and perhaps even throw in a little something to compensate for the trouble he caused you).
In addition, you should look at the seller's Audigon feedback. If his feedback is positive apart from your bad experience with him, it might be worth trusting that he'll send your money order back as promised. On the other hand, if his feedback has any negative comments at all, you might want to put a hold on the M.O. as others above have suggested. (I think there is a charge for this service, so if you decide to order a hold, you should ask him to pay this fee as well).
Finally, be sure leave some negative feedback on this guy describing what he did to you -- it seems very unfair. Maybe this will keep the same thing from happening to someone else. Hope this helps. Good luck. Don
