That I can agree with. Any realtor who even bothers to use comparables to price a home use homes that are better than the one they're pricing trying to inflate the value to get a higher commission. All it ends up doing is screwing over the buyer because the appraisal comes in low and the bank won't lend on the full amount. That being said realtors are usually within 10-20k when they make that kind of mistake. Zillow is usually much much worse than that. Worst pricing I've seen from zillow was a person who thought their shitty trashed house was worth 250k, over 30%, more than it was actually worth because it was the run down and smaller than everything else in the neighborhood.
Either way the blame gets put on the appraiser 9 times out of 10.