I've been both buying and selling on eBay for several years. This gives me a perspective on a situation like this from both sides. Buying on eBay will make you a better and more understanding seller, and vice versa. Basically, treat others like you want to be treated, and don't expect to find perfection in the world's biggest flea market.
This is not a situation that calls for neutral, negative, or anything lower than 5-star feedback. You got your item. A friendly message to the seller about how to improve their service for the future is recommended. The rating system is very unforgiving now; punishing a seller for a minor inconvenience is uncalled for.
For the buyer: the seller you are dealing with is probably more of a hobbyist seller. Very few businesses and individuals can exist solely by selling on eBay anymore. The fees are outrageous, and the entire process from photographing and listing an item to dealing with returns is very time-consuming and frustrating. Expecting every seller to ship for free and have your item within 3 days is unrealistic. If you think the shipping costs are too high, don't buy the item or factor the cost into your bid.
For the seller: ship quickly and upload the tracking information. There's no reason not to upload tracking ASAP whether you print your labels online or pay at the counter. Use the shipping method listed and ship in the time you say you will. Your buyer wants the item shipped quickly and securely. Happy buyers keep using eBay, and will be more likely to buy from you in the future.
In the past seven years I've left fewer than 10 negative feedbacks out of approximately 7,000 transactions, and all of them were extremely well deserved. Once was for a seller that refunded my payment because they wanted seven times the price I won the auction for. Another was for a lot of over $3,000 dollars worth of "scrap 14K solid gold" that was entirely 10K gold filled and electroplate. The seller refused to accept a return, forcing me to open a lengthy dispute which took weeks, and in the end I returned it and got my money back anyway.
Biggest complaints:
As a buyer: when the seller ends the auction early. The only reason to ever do this is if there is a serious problem with the listing (i.e., someone provides evidence that the item for sale is stolen, the item is destroyed in a fire or accident). 9 times out of 10 you will get more money if you let the auction run its course. Ending early completely wastes the time of buyers like me who don't bid until the last few hours or minutes. Use the buy it now format with best offer if selling quickly is your goal.
Runner up is listings with a five word description and five paragraphs of ridiculous terms of sale; most of these "terms" are superseded by eBay's own rules, and I'm not reading a novel so I can buy a $30 item that's poorly described.
As a seller: when buyers win or buy an item and don't pay. Particularly when the item is worth several hundred or thousand dollars. This is another absolute time-waster, and it requires several days to clear up before the item can be re-listed. I recently had someone drag their feet for 3 weeks and in the end I had to file a dispute so I could re-list the item.
Runner-up is buyers who have the wrong shipping address because they've moved or other reasons, then complain when the package doesn't arrive.
With the eBay platform: The site's interface is near completely unuseable. Over the past several years the "improvements" to the interface and search have made it slow and incredibly difficult to use the most basic functions. Every day I log in wondering if the site is going work at all.