You can put items you're interested in in your eBay cart to see if the seller offers combined shipping for more than one item. You'll see the total for shipping when you check out. If the listing doesn't say how much it will cost to ship extra items, you should contact the seller before making a payment to find out about options for combined shipping.
Most of the time, eBay sellers are happy to ship multiple items in one package. This is good for both parties. The buyer might get a shipping discount, and the seller saves money by combining shipments. But it's always best to check with the seller first to make sure you understand how shipping works and if there are any discounts for placing multiple orders.
If you have additional information or insights, don't hesitate to share in the comments.