For me I have found a few "tells" for kits.
Candy/bubble gum is one. I don't generally use sorbate so don't have a lot of experience with it, but I have at least one sorbated kit that didn't have a candy-ish taste so I know it doesn't _always_ cause it.
Most kits I have made, especially the reds, have a strange flavor. In most cases I can't identify a kit's varietals so whatever it is it makes kits taste unlike any other wine. They all sorta taste like blends of something I can't put my finger on. Also, some kits have specific strange flavors. For example, I can pick out some Cellar Craft Showcase kits I made 5 years ago from a single whiff because they have a strange aroma. Early on it was kinda like bananas but has evolved into something less describable.
But even more prevalent seems to be a flavor/aroma I can best describe as "musty". I find it in most kits, including whites. It tends to mute the flavors a bit, but I can pick it out even when it is subtle. I suspect this might be a result of the concentration process.
Anyway, I find using grapes, or fresh pressed white grape juice, tastes so much better that I have stopped making kits. YMMV.
Agree with others that barrel aging definitely improves kits significantly. For the record I use high vacuum to degass all my reds so residual CO2 is not an issue.