See it this way, your trader score is analogous to someone recommending a place, lets say a pizza place.
I may go to the pizza place every third day, because I absolutely love it. However, when I recommend it to someone, they consider it as one person recommending the place, right? So, 30 different people who may have gone there more than once each, recommend it to me, to me, it's 30 recommendations even though they've all had positive experienced say, 100 times courtesy that one place.
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Your total score is also visible, and that is for all individual sales.
Your trader score shows how many different people have had positive deals with you.