If I have a bad high school transcript(3.0) and currently have a 4.0 at my local university, will USC take that into consideration if I apply for a transfer with under 30 credits
I believe USC considers high-school transcripts, if you have less than 30 credits.
That is true ^^^.
Yup, they would want to see your HS transcripts and likely SAT/test scores if you’re under 30 units. I wonder how that would have worked for me if I had applied with under 30 units as I had neither. It took me two tries to get in, so by then I had something like 100 units.