UPS deals with the "customer" who placed the shippin
Actually, UPS deals with their customer, a.k.a. the person who paid them. Whether or not their customer (the seller/shipper) was reimbursed for the cost is of no matter to them.
USPS will deal with either for filing an initial claim, last I checked, but will need the physical receipt or electronic proof of the shipping, charges, and tracking that needs to come from the seller in most cases.
If you need a claim filed and the seller refuses to file it or provide the necessary receipts, go to your item's eBay page and put in a claim for "item not as described." Tell them what happened. With very little doubt, you'll get the claim filed because the seller won't want to lose the money and the item, as well as having that strike against their account.
As for sniping and the like, back when eBay was newer, I used to plan the days and times that I would list items. Sniping had to be done in person, and many buyers did it for reasons mentioned above, plus we had people that used to watch our bidding history because Rich and I would take the time to ferret out odd finds because of search terms like misspellings (we learned not to bid early pretty quickly lest we pay more than we had to). For example, I would never have auctions going off on a Friday or Saturday evening or night as a lot of people were out and about. Same with Sunday daytime. My best times were Tuesday, Wednesday and Thursday evenings between about 8 and 11PM which gave the left coast a chance to get out of work as well. There weren't any smart phones, so it had to be done from a computer! With sniping, smart phones, and the international side of eBay opening up, almost any time became a good time.
It's still the best game in town, not that it makes it any better. If you're careful about your search terms, show lots of pictures to protect yourself, and give good descriptions, your items will sell and you'll average less than 12% paid to eBay. Try to sell things and pay that low of a fee anywhere else!
Chuck