frequency and sumproduct

[step_one]

Im trying to use sumproduct to match by 2 different criteria

criteria
1) store #
2) invoice amount

to get the an order #

=SUMPRODUCT(--($E$2:$E$1508=A2),--($G$2:$G$1508=B2),--($F$2:$F$1508))

however....im struggling with to add logic (see highlight in yellow)

1)i was wondering if frequency can be used so it does not double count (see highlight in red)
(ie. invoice $36 is listed twice with store # 007....the sumprod will list the order # twice, however it only appears once in column F)

2) if invoice is listed twice $36 in column B, then check to see in column E & G is item is listed once under $70....is yes, then assign the code as $70/2 = $36


i would be very very grateful if someone can pls help!!

thxing u in advance.....