Seller Fees When a Coupon is Used

Good morning!

I recently sold my first model on the platform (which is super exciting!), but I was curious about the behavior of a coupon used by the customer that I wasn’t able to find an answer to via search engine or otherwise.

On checkout, the customer used a ‘20% off your first order’ coupon, bringing the $10 original price of the model down to $8. As this was not a coupon run by or directly authorized by me, I assumed sketchfab would eat that 20% off and I would earn $10 minus fees; however, I ended up eating the 20% myself, earning only $8 minus fees.

My question is, are all discounts run this way? Am I always eating whatever discount Sketchfab decides to run?
If there is an area that discusses seller guidelines more in depth I’d love to see it as the article(s) in the help centers didn’t seem to give a clear answer.

Thank you for the help!