I wouldn't rely on a commercial service to scan my negatives, especially if some of them are problematic. Commercial studio might be better equipped, but no one will devote the time and effort to optimize each negative on an individual basis; businesses normally don't do that unless paid handsomely, only an enthusiast will do it for the love of it (in a perverse twist in the English-speaking world the term "amateur" which comes from "love" got loaded with negative connotations while "professional", which is often a by word for the routine and the mediocre, with positive ones...) .
I wouldn't rely on a commercial service to scan my negatives, especially if some of them are problematic. Commercial studio might be better equipped, but no one will devote the time and effort to optimize each negative on an individual basis; businesses normally don't do that unless paid handsomely, only an enthusiast will do it for the love of it (in a perverse twist in the English-speaking world the term "amateur" which comes from "love" got loaded with negative connotations while "professional", which is often a by word for the routine and the mediocre, with positive ones...) .