Are Product and Market dimensions in your chart? You said there would be a Product selection, so only one Product will be selected at a time?
Selections are implied by default in Set Analysis. From what you describe, I don't know if you need Set Analysis.
In order to get overall Sales for a specific Market, you may need to use the TOTAL modifier:
Sum(TOTAL <Market> Sales)
That expression will give you the Sales for any Product in the Market of that record. Each time the Market appears in the chart it will have the same value.
I'm not sure if that is exactly what you are looking for. Could you provide some sample data, so we can get a better idea of what your data set looks like?