{7:9} And those whose scales weighed light - they are the ones who will have lost themselves as they used to do wrong with Our signs.
I think we need to work on "they used to do wrong with Our signs" since it sounds strange and doesn't capture the Arabic meaning.
Sure. I'm open to suggestions
I looked up all other occurrences, and it appears that this verse is the only one to use this particular idiom,
ظلم بـ. I consulted the exegesis of Ibn Katheer but it doesn't provide further insight into this idiom. Irving translates it as "because they have been damaging Our signs." That is the closest to my reading of it.
How about "
as they have been abusing Our signs." or something like it? This translation would also convey the meaning "as they used Our signs to do wrong instead of good." This understanding is actually validated and strengthened by the very next verse!
If you agree, then let me suggest this translation,
{7:9} And those whose scales weighed light - they are the ones who have lost themselves because they have been, with our Signs, unjust.