First time I got a roll developed and scan, a 1/3 of the photos weren't even on the CD. I went back and they said they'll rescan everything which they did but there was dust everywhere on the scans. Most of the subjects in my photos were covered in dust particles. It's pretty standard to blow air on the negatives to make sure there's no dust before scanning it.
Expect to go back 3 times to get a simple task done.