The main theme of 'A Roadside Stand' is that he is contrasting the lives of people who live in cities and those who live in the country.
The rich people from the city don't pay any attention to 'the roadside stands' which is where the poem got its name. It is set in India.
The stand is set up by a farmer who only wishes to earn a living by selling farm produce. He wishes to experience life as portrayed by the media. However no care ever stops to buy anything from the stand, and people even say how ugly it is. He spends his life waiting for cars to stop, only to receive harsh comments. He tells the drivers to keep their money if this is the way they feel.
Frost also puts his own feelings into the poem by saying that he can't bear the thought of the disappointed farmer, waiting all day for a car that never comes.
He ponders over the idea that it might be best just to put these people out of their misery, but then he comes to his senses.
I feel that this question will aid you greatly with the answer to this question as gives a critical analysis of the poem.