The supplier will send the items directly to the buyer, you only have to forward the order to the supplier.
How do you do that? You go to the supplier’s website and purchase the product with the buyers details, that’s it!
If there is a return, you have to inform your supplier about the return and forward the supplier’s instructions. To do so, the buyer will have to send the product to the supplier.
Once the supplier receives back the item, you will receive the corresponding refund. Once you receive the money, you can refund your buyer.