As a former seller on eBay and via my own website, I’ll add that although not everyone follows the same path, they have to make money somehow, and often aren’t really thoughtful about it. Shipping and payment options alone can overwhelm, and often the small vendors get chewed up by shippers and platforms like eBay.
At one time it got so crazy, I stopped charging for shipping, rolling shipping into prices. The price hawks squawked. Then I priced every item at $1, rolled it all into inflated shipping. The same customers complained about that.
My eventual solution was all prices were “straight up”, no 9.99 when we mean ten bucks, and all prices included flat rate postal shipping, and anyone wanting any other method was welcome to pay for the item, and send a prepaid label. Nobody ever did. I did have Canadians show up at my door at 11pm whining about wanting retail sales from a web only store. They paid the “shipping included” price, and I gave em a free Walmart bag . We are not buying or selling oxygen. Ain’t nobody who wasn’t rich to start with getting rich here.