On sites like this, your feedback is your reputation, and your reputation needs to be earned. If you want a good reputation, you do a good job. In this case, that means shipping the goods, well packaged, according to the time guidelines posted by the site or in the listing.
I don't leave negative feedback lightly, and I know that sometimes things go wrong. If something happens, and a shipment is late getting out, and I get a sincere apology and explanation from the seller, and possibly a partial refund, I'd most likely leave positive or neutral feedback.
In thos case, though, there are three strikes against the seller. He waited WAY too long to ship the package. Unless your listing says that you only ship once a month, or once a week, or something, I expect things to ship within a few days, especially if you advertise fast shipping. Then, when the OP complained about the shipping, he blamed the post office, when she had proof that it was his fault. And on top of that, he didn't even secure the package so it would arrive in good condition. Had just one of those things happened, I could see giving him a break, but all three is pretty good evidence that he's just not professional.
As a buyer, I would definitely want to know about this guy's lack of professionalism. I'm also not going to read through hundreds of positive feedback messages to find the ones that are actually negative. I skim the positives, and read the negatives and neutrals, and I really appreciate people giving honest feedback.
If he can't accept negative feedback, then he needs to improve his business practices, and earn positive feedback, not try to buy positive feedback from his customers.