Some of us don't just stick a stamp on it and put it in the closest mailbox. As a preference, I always go into the post office and talk with the rep and have them do my work. Sometimes, I pay for more than what I should and other times they put packages through that lack enough postage. Imagine if I would've put the incorrect postage on the package and put it in the closest mailbox....
Some are strict in how they ship, I am one of them. I have had many things returned even from going into the Post Office, thus they take responsibility for the issues. I had a package sent with tracking to the US that was guaranteed 5 business days, and it sat at the border for almost a full month, out of my hands on that one.
I've also been slow on shipping sometimes, but send out a PM and every time, the other person is OK with it. I've had one package in 5 years arrive with no cards, because it got demolished by the mail sorter, or the cards were thieved by the postal worker...I didn't blame the other trader for the issue, but they were nice enough to send replacements.
Prime example, I purchased a card before the postal strike at the end of May, it never arrived, and I got a refund. I dealt with the guy before and never assumed that he never sent out. If or when the card ever arrives, I will send him the Paypal once again.
I've yet to leave feedback for that one, but I would leave a positive because of the outcome.