Old thread, but isn't it possible that listing a domain on multiple marketplaces could get you into a bind? Lets say you list your domain on 5 different marketplaces, then by some awful stroke of luck the name sold on two of the marketplaces at the same time. Seems like this could get you into some sort of legal trouble.
It is tricky but can be done. For example, I have had Shrewd.com on eBay, dnforum and namepros at one time, but it's with a high BIN and make offer. It's very unlikely that someone would pay the BIN without making an offer on a $19K domain name. Also, one can list that it's multiforum post one inexpensive items, so that buyers know there's a slight chance it's already sold.
I am not a lawyer, but advertising is not a legal offer. In the old days of classifed ads in newspapers, you did not obviously have to sell a car you already sold. Likewise, if you are a store and run out of stock, you don't have to sell or even offer a raincheck what you advertised and are out of stock on. You will only get in trouble if you advertise a $10,000 new car and did not have a single new car to sell at that price.