Most people are pretty good on the EE, but sometimes there's a problem with different expectations between different people.
These are the guidelines I follow and what I expect from the people I deal with:
1. a) send the parcel or money order within 1 business day from when you made the agreement OR
b) let the other party know before closing the deal that you will be delayed for some reason. DO NOT just assume they will be willing to wait a week while you piss around.
2. a) When you ship a parcel PM the tracking number to the other party on the same day AND
b) keep the post office reciept with the tracking number in a safe place until you know the package has arrived safely at the destination.
3. If you send a parcel, then stay available for communications until the parcel reaches the destination. It's not really clever planning to take a 3 week holiday the day after you ship a package, BUT IF YOU MUST BE AWAY then let the receiver know about it up front.
4. The person receiving the package or money order will PM the sender when it has arrived.
5. if the other party to your deal is trying to contact you to tell you something is wrong, then ANSWER the PM or email even if you don't have an immediate remedy, so that the other party knows you're not running away and hiding. The other person can see when you were online, so he will know that you read and ignored his questions. It is incredibly annoying to have a package 2 weeks late and know that the person who sent it is reading your PMs but not answering them. Don't be that jerk.
6. If you PM the seller to say "I'll take it", but then change your mind - send a PM and tell him you changed your mind. DON'T just go quiet and hide out hoping he goes away. BETTER YET - make up your mind BEFORE you start making promises you can't keep. It makes you look dumb.
Let the other person know what you are doing. If you are delayed then let the other party know. Send the tracking number without being asked. Keep yourself available and check PMs regularly until the deal is complete in case there is a problem so the other party can contact you. Acknowledge when the package arrives.