Agreed; they often come in JPG or TIFF format scanned on Noritsu's, which is already lossy in detail, and 24-bit color depth only (16.7M colors)
Too bad they don't offer them in RAW format so you can do it yourself (maybe some do?)
If they are smart they should offer RAW files from Noritsu. It would save them some time when scanning. But files are big. Maybe labs could take your USB key and copy the raw files on it when you come to pick up your negatives.
Home 35mm scanners are capable of 48-bit color, even RAW. allowing more capability to adjust to your liking, just like your digital camera RAW files.
I would never trust a lab scan's color accuracy.
Here, a Noritsu raw file (135 format at highest resolution). Have a go and tell us how many users would you trust to come up with better colours than this: