Is there a professional out there who can speak to this? I'd simply like to know from a pro how frequently cooking oil is really changed at mid-level eating places. Please don't tell me there is no problem if the oil is replaced at regular intervals — that's the crux of my wife's argument: they don't replace the oil at regular intervals, they just add to it as it's used up.
The lady is a little neurotic on this subject. For deep frying at home, she buys the cheapest super-market oil she can find and uses it once. That causes me great pain — I mean the part about using it once.