It depends on how the sales amount was used. If it was used in addition then the wrong amount has to be subtracted first and the correct amount added. That is, -350+530=180 has to be added.
The signs are reversed if the amount was used in subtraction --- +350-530=-180 has to be added, which is the same as subtracting 180.
If the amount was used in multiplication, then the multiplication has to be reversed by dividing by the wrong amount and multiplying by the correct amount. That is, multiplying by the fraction 530/350=53/35.
If the amount was used in division then the fraction is inverted: 350/530=35/53.