try using if(indicator == "A", salesquantity*price1,salesquantity*price2).
The operator info states:
Beside those operators and functions, this operator also supports the constants pi and e if this is indicated by the corresponding parameter (default: true). You can also use strings in formulas (for example in a conditioned if-formula) but the string values have to be enclosed in double quotes.
To read it, use the context menu in the operator tree or press F1.