An acquaintance was telling me about the shops in the country she is living in. There, courtesy is utmost, they will never tell you "no". If she asked for a certain product, they would never say "no", but always "yes", but tell you with their expression that "no, we don't have it".
Until she learned to read what the expression said, not the words, she found it very awkward.
With this shop owner you have found the polar opposite, if you ask for a product the shop does not carry, they demean you for wanting what they don't have.