Count duplicates very difficult.

Hi
Try this formulas

Formula:

=SUMPRODUCT(--($C$5:$C$17=$F5)*((D$5:D$17<>"")))*(COUNTIF(C$5:C$17,$F5)=2)

Formula:

=SUMPRODUCT(--($C$5:$C$17=$F5))*(COUNTIF($C$5:$C$17,$F5)=3)/3

Formula:

=SUMPRODUCT(--($C$5:$C$17=$F5))*(COUNTIF(D$5:D$17,$F5)=4)/4

Where F5:F11 are the Customer
See the file