How is your listing set up?
If you have it based on the weight of the item then for multiple purchases eBay will add the weights together and bill shipping based on that total weight.
One problem becomes if the multiple items on a single box exceed 1 cubic foot. Then you might find it cheaper to send 2 smaller boxes than 1 big box.
OR your item is designed to go first class mail, but several in a single package goes over 16 ounce and automatically kicks it into a 2 pound Priority Mail package. Again, compare the price of shipping each or a few in different FCM packages.
"Laissez-faire capitalism (AKA The Great Material Continuum) is the only social system based on the recognition of individual rights and, therefore, the only system that bans force from social relationships." ~ Ayn Rand
