Answer:
line 12 in what article? you don't have any excerpts
The answer would be “but” since it contrasts his motivation with competing with others for a high score.
Hopefully this helped.
Explanation:
I think the question is wrong. Sorry if I am wrong!
But It should have been "You cannot get a refund ________ sale goods."
In this case the answer should have been ON.
Anyway the answer is ON.