Why does the traveling salesman take an interest in Elisa's chrysanthemums?
The only reason the tinker (the traveling salesman) takes interest in Elisa's chrysanthemums is because he is trying to get her business! He is trying to get her to give him some pots to mend. SO, he is merely lying and being deceitful in order to make some money. We know this because he has thrown her chrysanthemum in the road at the end of the story, and Elisa sees this and breaks down and cries.