The customers that bought one watermelon bought 1 * 17 = <<1*17=17>>17 melons.
The customers that bought three melons bought 3 * 3 = <<3*3=9>>9 melons.
The stand sold 46 - 17 - 9 = <<46-17-9=20>>20 melons to customers who bought 2 melons.
Thus, 20 / 2 = <<20/2=10>>10 customers bought two watermelons.
#### 10