Why suddenly low commission rate for 1 sale?

I made 2 sales 3 days back and now today i got the 3rd sale and it says I just got $13.5 commission instead of regular $25 per sale.

Why is that? I am new to clickbank now quite sure and even it shows "3" under the items colum

What does it mean

PS: There was no chargeback or refund issued and it was just a normal sale but why the commission low just for that sale

Many times, customers can get a discounted price. (hitting the back button, popup happens, stay on page and get a discount)

So it's possible that the first 2 sales, people payed full price.
But the 3rd sale someone got a discount. And then you got a commission percentage based on that discount.

That's how it is for me anyways

Oh i see. But that guy bought that in 3 nos as it reflects "3" under items
Anyways i just checked and they are offering insane discount for those who go back

Well, maybe they offer insane discount, but if they did not do this the customer would have left the site and never bought anything. This way at least you got $13 instead of $0. Exit scripts can be sometimes really helpful.