In the automotive world, there are some parts that just aren't available brand new and so we offer them as a reconditioned, or remanufactured item.

In order to obtain used parts (cores) to rebuild and resell, we must impose an additional charge (a core deposit) on top of the purchase price of a part.
You as a buyer pay this core deposit at the time of purchase. After receiving the new part, you send back your old part, or "core."
Once the core is returned to us, we'll inspect it to ensure it is in a rebuild-able condition, then we will refund the core deposit back to you.

In the end, core deposits help us to obtain stock to rebuild, but they also help our customers to be able to buy the parts they need and not be off the road waiting for their part to be reconditioned.