Previously being a powerseller myself my take on leaving feedback varies from customer to customer. I mainly sell high grade comic books, so condition is of utmost importance. I've never had any bad situation personally, but I have heard many of the horror stories from fellow collecting buddies of mine across the country who have had buyers switch books on them or claim to have never received an item, etc. Is the buyer's only responsibility to make a payment?
For instance, I remember having a buyer from New York who sent me a paypal payment, which had a confirmed address. I sent the item out via USPS Priority insured with delivery confirmation. Two days later, paypal emails me stating that they have reason to believe that the buyer sent funds from a stolen credit card and that the funds that I received have been reversed and taken out of my account! Out of sheer dumb luck, I received the package I sent him because the address was a little off and the person at the incorrect adress refused the delivery. I calmly emailed the buyer explaining what had happened and that I wanted him to pay for my ebay fees and postage fees and to my surprise he sent me a money order as promised. Would I have been so lucky if I left a positive right away? I highly doubt it. After speaking to the rightful owner of the credit card, which was his grandmother, I discovered that this person was out on parole and that she was so ashamed of what he has and had done again!
You can take that to the bank!