Except it's not. If there were no defects, there would be no defects reported on the forums. The number of cars sold is public.

The parent isn't suggesting looking at the ratio of happy and sad posters, which would definitely be selection bias, they are saying look at the rate and severity of complaints on it's own.

If you have a defect you are about 1000x more likely to go to the forum.

Of course there are defects, at that volume that would be expected.

Parent didn't say anything about rates.