When I buy single balls they are shipped with the ball box from the manufacturer inside a 9"x9"x9" cardboard box often made by Uline.
I save all those boxes to ship (double boxing is essential as far as I am concerned) sold used and new balls.
I have an online account with both UPS and FEDEX, using a credit card. That gives me a small discount vs someone who has none. (People who work for a company that has a large business account with either shipping company will obviously get a larger discount.)
When I sell a ball I often ship UPS because they have many stores with convenient store fronts with whom I can drop off the sealded box with a sticker with the delivery and return address and the bar code generated by their website, for no charge. For FEDEX I have to bring it to their local office or a drop off store front (less convenient for me than UPS. FEDEX can be slightly cheaper.
"None are so blind as those who will not see."
"Some bowlers are crazy as pickled cats."