I bought two tf cards at Tmall and got one. What if the store refuses to admit it?

There is no way to prove this.

You think as usual. For example, I bought two precious stones, worth 654.38+ ten thousand.

You signed for it without reading it, and then you went to someone else and said it was short. Who admitted it?

It's all right to sign for the express delivery. Signing indicates that the quantity and items purchased are normal and correct.