I've been reading this thread with fascination, amazed that people will actually try to pull off things like that. I hate to think I'm that gullible, because usually I am not, but I tend to take a restaurant or grocer at their word unless it's obviously not so. A few experiences, both pro and con, I've had:
- Any number of restaurants advertising "crab-stuffed" anything, or any sort of crab in a sauce preparation, using imitation crabmeat instead.
- A vendor at the farmers' market who got tossed out on his ear after his "locally grown" peaches were found to have been brought in from the Rio Grande valley, which isn't very local, by about 800 or so miles.
- A purveyor of "farm-raised" pork, beef and lamb who apparently was selling more than he grew, and supplementing it with purchased meat. He's actually doing fed time on a related offense.
- On the other side of the equation, a restaurant in a town where I once lived advertised wagyu beef. I went to dinner there one night, and was cautioned by the waiter that they wagyu steak wasn't wagyu, as the chef/owner had looked at the shipment and rejected it, going with Kobe that night instead.
And on the butter/margarine issue -- I used to belong to an organization that sold Maine lobsters, either live, cooked on-site, or the frozen tails. For the cooked on-site, we included corn, potatoes and melted butter. One year, whoever bought the groceries for the event bought margarine instead. I came unglued when some of the cooks suggested to me it didn't make any difference, and went to the store myself and got butter.
Margarine is nasty stuff. I'll use it when I'm eating at my favorite local greasy spoon meat-and-three, because they don't offer butter, but that's about it.