Why do my items with no cost have negative margin %s?

Can someone explain why having having a product with no cost come up as 0% margin instead of 100%?

Things like boarding (which has no cost for us) are bringing the margin down.
Any insight would be greatly appreciated!

-Josh

@TheBeastiary i am not certain, but I could be that a non-existing cost will be interpreted as if the product price is the cost (kind of fallback value).

Did you try assigning a value of 0,01?