Amazon has been authorizing full refund on orders with no return needed. We did not authorize this how do you stop it.
Obviously you should check your settings to make sure you have not approved any rules about returnless refund.
Other than that – were these transactions under $10?
No approved return less refund rules and orders were over $10
Did you authorize the buyers return request within 48 hours? If you do not and the buyer complains, Amazon will issue a full refund and let the buyer keep the product.