I am breaking the World Series hiatus because this story was too much to keep quiet about:
According to this interview up to 48% of fish served in restaurants in the Boston area are not the species reported on the menu. Percentages for mislabeled fish in Grocery stores was much lower, but is still an annoyingly high 15% .
Both of these studies were done in the particularly Seafood savvy markets of Boston, and here in the PNW. I shudder to think what the percentages are in parts of the country where the chances of a commercial fisherman walking in off the street is much lower.
Substituting tilapia for red snapper is ridiculous! Tilapia is a fresh water fish, and looks, tastes, and cooks nothing like snapper. Red Snapper is incredibly overfished. If there is so much goo on it that you can't tell the difference between those two then stop using (or pretending to use) such high demand species. Just tell people the truth.
Ask questions, know your fish, buy whole when you can, and shop at reputable purveyors.