As an eBay buyer or seller, it is educational to use the shipping calculator to compare various shipping methods.
https://www.ebay.com/shp/Calculator
The calculator is not easy to find on the eBay website. It is ALWAYS better to use Google to find important and useful information on the eBay site. The eBay website is a mess, with bugs that are never fixed, and they are constantly changing it and adding new bugs to go with the old ones.
As a buyer, if you have a fairly good idea of the size and weight of the shipment, using the calculator can detect sellers who overcharge you for shipping. This is very common, and also beware of “handling charges”.
Honest sellers will charge the buyer exactly what eBay charges them to ship.
As a seller, you can compare various shipping methods, including the USPS, UPS, and FedEx. It tells you the discount you get on the over the counter price for each service. The caveat with UPS and FedEx is that what you may end up being charged something other than what the calculator tells you. They do check the weight and package size after shipment.
I know of one crooked eBay seller who routinely understated the weight of packages when buying shipping labels to save money. Eventually, the USPS caught up with him and sent him a bill for the difference. If you drop off packages at the counter, they check the weight. But if you drop packages into a bin, the check happens later. Having a package scanned at the counter is better as it puts an entry into the tracking record “USPS in possession of item”.
Thanks - I just now tried the link you gave: It came back with the same shipping cost, $2.04, via. “USPS First Class Mail Large Envelope 2 to 5 business days, as when I made up a trial (only set it up part way) listing. That link is helpful because I can check the shipping without having to start an actual listing. :-)