Shipping Costs for Phone Covers?

Could someone help me understand how people sell phone cases online like walmart, amazon, ebay etc and still make money? If the phone case is like $10 to buy the shipping will be like $2-$4 right? Do people really pay $4 to ship a single phone case?

if they ship it with tracking number it cost more than 4 $, without tracking number , you have to pay only the stamps depending on destination country and weight

Simply, the cases can cost around 0.50 cents when the seller buys them in large quantities. and shipping is always paid for by the customer. When you sell an item for a cheap price like a cellphone case, its the type of products that move in large quantities, although you don't make much per item, but money starts adding up.