Sum based off condition

Hi all,

I am trying to create a column that will sum two other columns based off a condition & cannot seem to get it correct. for example heres what the data looks like:

CustomerID      Product   Sales   Sales2

1                          fruit          500

2                          veggi       100        200

3                          veggi       50           200   

4                           fruit         150

the goal is create a column called sales3 that when the product = fruit it will return the Sales column and when the product = veggi it will only return sales2 column.

what is the best way to achieve this?

thank you