The shop that sold questions

An original fictional scene set in an imaginary shop.

There were no goods in the window, only three cards. One asked where a road ended. Another asked whether a promise expired. The third had been turned face down. A small notice said that prices depended on the question, not on the length of the answer.

Inside, the shopkeeper was dusting an empty shelf. I asked what he sold. He pointed towards a jar marked First Questions, then waited. I could not tell whether he was joking or whether I had already agreed to buy something.

I asked how much the jar cost. He said the jar was not for sale. The silence that followed seemed to leave my words standing on the counter between us. I put my hands in my pockets, although I had taken no money out.

As I turned to leave, he asked what I had expected to find. This was the first question he had offered me, and I was suddenly reluctant to answer it quickly. Outside, the face-down card in the window still looked more expensive than the others.

How does the writer make the shop seem puzzling to the narrator?