Selling to external market in Brass, is benefit salary or cash?
The extra amount is in additional income, in squares. According to the publisher's website:


  if you sell to the Distant Market then the additional income shown on the Cotton Demand track is added to your income level, it is not taken as cash.


And further on, clarifying that you go up by squares, not bands:


  When you gain income you go up a number spaces equal to the income increase, e.g. if you gained £5 then you would go up five spaces. Note that this does not translate into an increase of £5 in actual income, as that depends on the income band you are in.


The bands are only used when reducing your income due to taking loans.