FEEDBACK FORUMIf you feel you've been wronged in an EE transaction, start a thread and let the EE mods assist you.
This is helpful both for you in resolving your issue, but also for the rest of the EE users on this site to help weed out the bad apples and make the EE a more trustworthy place to do business.
As to your deals:
In case one, you were a bit too trusting to send the goods without payment, but should payment still fail to arrive and the buyer stops communicating, its a big deal and deserves attention.
In case two, EE rules stipulate that the seller is responsible for getting the goods to the buyer. If this fails due to poor packaging as it sounds in your case, it is up to the seller to make you whole (refund or replace the item) and then the seller has to start an investigation with the USPS since they sent the package. Sounds like you already came to an agreement with the other party so likely nothing you can do now, but know that per the EE rules, you should have been made whole by the seller.
In case three, if the seller remains unresponsive for several days and won't answer emails or IM's start a thread and get the EE mods to help.
The Arfcom EE has become my favorite and preferred place to buy and sell odds and ends because of how it is laid out and staffed by dedicated mods who help to resolve issues should they arise, but the system only works if everyone follows the rules AND brings problems to the attention of the staff so that they can be worked out, or failing a resolution, the at fault parties can be removed from the site.