Regarding drop-shipping from China - I have samples sent to me to confirm that they are shipping a genuine product.

Do you not think that if they are selling counterfeit items and you asked for a sample they may just send you a genuine one and then send out fakes to your buyers? You wouldn't be the first one to be caught out by that trick. if I were you I would get a friend or relative to blind purchase one just to check it is the real deal.

If they did turn out to be fakes then it is you who will be left out of pocket, you will probably have to refund without return and you will have no chance of getting your money back from the supplier.

In this instance if the buyer wants a full refund I would ask them to send the phone back and you will pay the postage.