I found out when I unknowingly bought a censored version of an album from
Walmart. There was no label on the CD itself & no signage in the store saying that they sell only edited versions. Maybe Walmart regulars just "know" these types of things, but I rarely shopped there & had no idea. I only realized it when I saw the same CD at another store & there were two versions - one with a "Parental Advisory" sticker on it and one labeled "Clean Version." So, at least at my local Walmart, it was a "secret" in that there was no labeling or signage to inform customers that they were buying an edited product.
ETA: IIRC, this was in the early 2000s.