It could probably be done -- but it would only check when the ad was started, so if the user had 1 open conversation slot when he started the ad, and it filled up the first day, you would still have an ad with no pm ability.
Yes that's true but as soon as the seller tries to respond (to the buyer) he would automatically be informed that his/her PM box is full which would keep him from selling his parts!! This would force him/her to clear his box so that he can continue to try and sell/buy/trade??
