I used to work retail and saw scammers try to pull the same trick many times. One time a guy bought a new Xbox 360 and came back an hour later with an old, obviously used, and dirty original Xbox claiming it was in the box.
This happened with some devices which had their serials scanned too, through a hole in the box so we know the real item was bought, and the person would swear up and down and raise hell, call corporate, etc. trying to convince us otherwise. It's amazing the lengths some people go through to really sell their con to the public.
We also had lots of people bringing in a broken unit that matched the box, but serial number was off.
For every legitimate story - and im sure by sheer chance there must be a handful around the country - there are 10,000 scammers.
With open items (that are bought as open items), I think there is a small chance the person doing the return wasn't looking and made a mistake. With brand new items I think it's the consumer pulling a scam 99.99999% of the time.
Talking about it in public and saying things like "if I was scamming I wouldn't be complaining" is just a gimmick to add to the credibility of the con because it makes people think "gee, maybe he is legit" and second guess themselves.
Going public could also be used by the con man to go back to the store and say "if I was a scammer I wouldn't be posting publicly about this" to try to get a manager to go along with it by second guessing themselves or fearing public backlash and bad publicity.
My advice: if you are buying something big ticket and you really worry about this, pay for it and then open it while still at the store to examine it. That way, if there's a problem it's easier to prove.