If it's from a big pet store, it's probably a no. Hets are more costly than normals, and if they're buying BPs, they're getting something cheap to re-sell for higher, and if they're going to get something not-normal, it'll be visual, because the average customer will not pay more for a snake that looks the same.

If it's from a smaller store, they probably keep records. Mine does; if they buy a het from a breeder, they write it down and factor that into the costs- and rightly so. i.e. the store I got my rats from had cards on the snake's enclosures saying "enchi het pied".

If it's from someone else, and they didn't mention anything, it's probably not.

If no one knows the origin, i.e. my female normal was a rescue from Hurricane Katrina, then no one knows and hey, it very well could be- but probably not.