This is called the "Amazon effect". Where online buyers expect all orders to be in the stock, ship right away for free and show up within 2 days.
This actually is a real thing.
THIS IS THE TRUTH RIGHT HERE.
and advertise "free shipping" because it attracts buyers and free shipping is what the lions share of Ebay buyers want.
Yes this, especially for competitive items. However, people also are afflicted by the immediacy syndrome (see first quote, above) and some items that won't sell at auction will sell quickly for "buy it now." Regardless of shipping method.
I won't buckle on my shipping practices. I do well enough moving stuff to do it my way to my own satisfaction.
Remember the ebay 99 cent gimmick? They promoted this as a way to start auctions to generate more interest. That died rather quickly. When too many things more valuable than 99 cents got gobbled up for that price. Do not listen to their marketing advice. If you've got something worthy of sale, properly priced, it will move. You don't have to be the "popular kid" on ebay to make it work.